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• Implicit conversion : const reference vs non-const reference vs non-reference

  - by Nawaz

  Consider this code, struct A {}; struct B { B(const A&) {} }; void f(B) { cout << "f()"<<endl; } void g(A &a) { cout << "g()" <<endl; f(a); //a is implicitly converted into B. } int main() { A a; g(a); } This compiles fine, runs fine. But if I change f(B) to f(B&), it doesn't compile. If I write f(const B&), it again compiles fine, runs fine. Why is the reason and rationale? Summary: void f(B); //okay void f(B&); //error void f(const B&); //okay I would like to hear reasons, rationale and reference(s) from the language specification, for each of these cases. Of course, the function signatures themselves are not incorrect. Rather A implicitly converts into B and const B&, but not into B&, and that causes the compilation error.

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• Error in running script [closed]

  - by SWEngineer

  I'm trying to run heathusf_v1.1.0.tar.gz found here I installed tcsh to make build_heathusf work. But, when I run ./build_heathusf, I get the following (I'm running that on a Fedora Linux system from Terminal): $ ./build_heathusf Compiling programs to build a library of image processing functions. convexpolyscan.c: In function ‘cdelete’: convexpolyscan.c:346:5: warning: incompatible implicit declaration of built-in function ‘bcopy’ [enabled by default] myalloc.c: In function ‘mycalloc’: myalloc.c:68:16: error: invalid storage class for function ‘store_link’ myalloc.c: In function ‘mymalloc’: myalloc.c:101:16: error: invalid storage class for function ‘store_link’ myalloc.c: In function ‘myfree’: myalloc.c:129:27: error: invalid storage class for function ‘find_link’ myalloc.c:131:12: warning: assignment makes pointer from integer without a cast [enabled by default] myalloc.c: At top level: myalloc.c:150:13: warning: conflicting types for ‘store_link’ [enabled by default] myalloc.c:150:13: error: static declaration of ‘store_link’ follows non-static declaration myalloc.c:91:4: note: previous implicit declaration of ‘store_link’ was here myalloc.c:164:24: error: conflicting types for ‘find_link’ myalloc.c:131:14: note: previous implicit declaration of ‘find_link’ was here Building the mammogram resizing program. gcc -O2 -I. -I../common mkimage.o -o mkimage -L../common -lmammo -lm ../common/libmammo.a(aggregate.o): In function `aggregate': aggregate.c:(.text+0x7fa): undefined reference to `mycalloc' aggregate.c:(.text+0x81c): undefined reference to `mycalloc' aggregate.c:(.text+0x868): undefined reference to `mycalloc' ../common/libmammo.a(aggregate.o): In function `aggregate_median': aggregate.c:(.text+0xbc5): undefined reference to `mymalloc' aggregate.c:(.text+0xbfb): undefined reference to `mycalloc' aggregate.c:(.text+0xc3c): undefined reference to `mycalloc' ../common/libmammo.a(aggregate.o): In function `aggregate': aggregate.c:(.text+0x9b5): undefined reference to `myfree' ../common/libmammo.a(aggregate.o): In function `aggregate_median': aggregate.c:(.text+0xd85): undefined reference to `myfree' ../common/libmammo.a(optical_density.o): In function `linear_optical_density': optical_density.c:(.text+0x29e): undefined reference to `mymalloc' optical_density.c:(.text+0x342): undefined reference to `mycalloc' optical_density.c:(.text+0x383): undefined reference to `mycalloc' ../common/libmammo.a(optical_density.o): In function `log10_optical_density': optical_density.c:(.text+0x693): undefined reference to `mymalloc' optical_density.c:(.text+0x74f): undefined reference to `mycalloc' optical_density.c:(.text+0x790): undefined reference to `mycalloc' ../common/libmammo.a(optical_density.o): In function `map_with_ushort_lut': optical_density.c:(.text+0xb2e): undefined reference to `mymalloc' optical_density.c:(.text+0xb87): undefined reference to `mycalloc' optical_density.c:(.text+0xbc6): undefined reference to `mycalloc' ../common/libmammo.a(optical_density.o): In function `linear_optical_density': optical_density.c:(.text+0x4d9): undefined reference to `myfree' ../common/libmammo.a(optical_density.o): In function `log10_optical_density': optical_density.c:(.text+0x8f1): undefined reference to `myfree' ../common/libmammo.a(optical_density.o): In function `map_with_ushort_lut': optical_density.c:(.text+0xd0d): undefined reference to `myfree' ../common/libmammo.a(virtual_image.o): In function `deallocate_cached_image': virtual_image.c:(.text+0x3dc6): undefined reference to `myfree' virtual_image.c:(.text+0x3dd7): undefined reference to `myfree' ../common/libmammo.a(virtual_image.o):virtual_image.c:(.text+0x3de5): more undefined references to `myfree' follow ../common/libmammo.a(virtual_image.o): In function `allocate_cached_image': virtual_image.c:(.text+0x4233): undefined reference to `mycalloc' virtual_image.c:(.text+0x4253): undefined reference to `mymalloc' virtual_image.c:(.text+0x4275): undefined reference to `mycalloc' virtual_image.c:(.text+0x42e7): undefined reference to `mycalloc' virtual_image.c:(.text+0x44f9): undefined reference to `mycalloc' virtual_image.c:(.text+0x47a9): undefined reference to `mycalloc' virtual_image.c:(.text+0x4a45): undefined reference to `mycalloc' virtual_image.c:(.text+0x4af4): undefined reference to `myfree' collect2: error: ld returned 1 exit status make: *** [mkimage] Error 1 Building the breast segmentation program. gcc -O2 -I. -I../common breastsegment.o segment.o -o breastsegment -L../common -lmammo -lm breastsegment.o: In function `render_segmentation_sketch': breastsegment.c:(.text+0x43): undefined reference to `mycalloc' breastsegment.c:(.text+0x58): undefined reference to `mycalloc' breastsegment.c:(.text+0x12f): undefined reference to `mycalloc' breastsegment.c:(.text+0x1b9): undefined reference to `myfree' breastsegment.c:(.text+0x1c6): undefined reference to `myfree' breastsegment.c:(.text+0x1e1): undefined reference to `myfree' segment.o: In function `find_center': segment.c:(.text+0x53): undefined reference to `mycalloc' segment.c:(.text+0x71): undefined reference to `mycalloc' segment.c:(.text+0x387): undefined reference to `myfree' segment.o: In function `bordercode': segment.c:(.text+0x4ac): undefined reference to `mycalloc' segment.c:(.text+0x546): undefined reference to `mycalloc' segment.c:(.text+0x651): undefined reference to `mycalloc' segment.c:(.text+0x691): undefined reference to `myfree' segment.o: In function `estimate_tissue_image': segment.c:(.text+0x10d4): undefined reference to `mycalloc' segment.c:(.text+0x14da): undefined reference to `mycalloc' segment.c:(.text+0x1698): undefined reference to `mycalloc' segment.c:(.text+0x1834): undefined reference to `mycalloc' segment.c:(.text+0x1850): undefined reference to `mycalloc' segment.o:segment.c:(.text+0x186a): more undefined references to `mycalloc' follow segment.o: In function `estimate_tissue_image': segment.c:(.text+0x1bbc): undefined reference to `myfree' segment.c:(.text+0x1c4a): undefined reference to `mycalloc' segment.c:(.text+0x1c7c): undefined reference to `mycalloc' segment.c:(.text+0x1d8e): undefined reference to `myfree' segment.c:(.text+0x1d9b): undefined reference to `myfree' segment.c:(.text+0x1da8): undefined reference to `myfree' segment.c:(.text+0x1dba): undefined reference to `myfree' segment.c:(.text+0x1dc9): undefined reference to `myfree' segment.o:segment.c:(.text+0x1dd8): more undefined references to `myfree' follow segment.o: In function `estimate_tissue_image': segment.c:(.text+0x20bf): undefined reference to `mycalloc' segment.o: In function `segment_breast': segment.c:(.text+0x24cd): undefined reference to `mycalloc' segment.o: In function `find_center': segment.c:(.text+0x3a4): undefined reference to `myfree' segment.o: In function `bordercode': segment.c:(.text+0x6ac): undefined reference to `myfree' ../common/libmammo.a(aggregate.o): In function `aggregate': aggregate.c:(.text+0x7fa): undefined reference to `mycalloc' aggregate.c:(.text+0x81c): undefined reference to `mycalloc' aggregate.c:(.text+0x868): undefined reference to `mycalloc' ../common/libmammo.a(aggregate.o): In function `aggregate_median': aggregate.c:(.text+0xbc5): undefined reference to `mymalloc' aggregate.c:(.text+0xbfb): undefined reference to `mycalloc' aggregate.c:(.text+0xc3c): undefined reference to `mycalloc' ../common/libmammo.a(aggregate.o): In function `aggregate': aggregate.c:(.text+0x9b5): undefined reference to `myfree' ../common/libmammo.a(aggregate.o): In function `aggregate_median': aggregate.c:(.text+0xd85): undefined reference to `myfree' ../common/libmammo.a(cc_label.o): In function `cc_label': cc_label.c:(.text+0x20c): undefined reference to `mycalloc' cc_label.c:(.text+0x6c2): undefined reference to `mycalloc' cc_label.c:(.text+0xbaa): undefined reference to `myfree' ../common/libmammo.a(cc_label.o): In function `cc_label_0bkgd': cc_label.c:(.text+0xe17): undefined reference to `mycalloc' cc_label.c:(.text+0x12d7): undefined reference to `mycalloc' cc_label.c:(.text+0x17e7): undefined reference to `myfree' ../common/libmammo.a(cc_label.o): In function `cc_relabel_by_intensity': cc_label.c:(.text+0x18c5): undefined reference to `mycalloc' ../common/libmammo.a(cc_label.o): In function `cc_label_4connect': cc_label.c:(.text+0x1cf0): undefined reference to `mycalloc' cc_label.c:(.text+0x2195): undefined reference to `mycalloc' cc_label.c:(.text+0x26a4): undefined reference to `myfree' ../common/libmammo.a(cc_label.o): In function `cc_relabel_by_intensity': cc_label.c:(.text+0x1b06): undefined reference to `myfree' ../common/libmammo.a(convexpolyscan.o): In function `polyscan_coords': convexpolyscan.c:(.text+0x6f0): undefined reference to `mycalloc' convexpolyscan.c:(.text+0x75f): undefined reference to `mycalloc' convexpolyscan.c:(.text+0x7ab): undefined reference to `myfree' convexpolyscan.c:(.text+0x7b8): undefined reference to `myfree' ../common/libmammo.a(convexpolyscan.o): In function `polyscan_poly_cacheim': convexpolyscan.c:(.text+0x805): undefined reference to `mycalloc' convexpolyscan.c:(.text+0x894): undefined reference to `myfree' ../common/libmammo.a(mikesfileio.o): In function `read_segmentation_file': mikesfileio.c:(.text+0x1e9): undefined reference to `mycalloc' mikesfileio.c:(.text+0x205): undefined reference to `mycalloc' ../common/libmammo.a(optical_density.o): In function `linear_optical_density': optical_density.c:(.text+0x29e): undefined reference to `mymalloc' optical_density.c:(.text+0x342): undefined reference to `mycalloc' optical_density.c:(.text+0x383): undefined reference to `mycalloc' ../common/libmammo.a(optical_density.o): In function `log10_optical_density': optical_density.c:(.text+0x693): undefined reference to `mymalloc' optical_density.c:(.text+0x74f): undefined reference to `mycalloc' optical_density.c:(.text+0x790): undefined reference to `mycalloc' ../common/libmammo.a(optical_density.o): In function `map_with_ushort_lut': optical_density.c:(.text+0xb2e): undefined reference to `mymalloc' optical_density.c:(.text+0xb87): undefined reference to `mycalloc' optical_density.c:(.text+0xbc6): undefined reference to `mycalloc' ../common/libmammo.a(optical_density.o): In function `linear_optical_density': optical_density.c:(.text+0x4d9): undefined reference to `myfree' ../common/libmammo.a(optical_density.o): In function `log10_optical_density': optical_density.c:(.text+0x8f1): undefined reference to `myfree' ../common/libmammo.a(optical_density.o): In function `map_with_ushort_lut': optical_density.c:(.text+0xd0d): undefined reference to `myfree' ../common/libmammo.a(virtual_image.o): In function `deallocate_cached_image': virtual_image.c:(.text+0x3dc6): undefined reference to `myfree' virtual_image.c:(.text+0x3dd7): undefined reference to `myfree' ../common/libmammo.a(virtual_image.o):virtual_image.c:(.text+0x3de5): more undefined references to `myfree' follow ../common/libmammo.a(virtual_image.o): In function `allocate_cached_image': virtual_image.c:(.text+0x4233): undefined reference to `mycalloc' virtual_image.c:(.text+0x4253): undefined reference to `mymalloc' virtual_image.c:(.text+0x4275): undefined reference to `mycalloc' virtual_image.c:(.text+0x42e7): undefined reference to `mycalloc' virtual_image.c:(.text+0x44f9): undefined reference to `mycalloc' virtual_image.c:(.text+0x47a9): undefined reference to `mycalloc' virtual_image.c:(.text+0x4a45): undefined reference to `mycalloc' virtual_image.c:(.text+0x4af4): undefined reference to `myfree' collect2: error: ld returned 1 exit status make: *** [breastsegment] Error 1 Building the mass feature generation program. gcc -O2 -I. -I../common afumfeature.o -o afumfeature -L../common -lmammo -lm afumfeature.o: In function `afum_process': afumfeature.c:(.text+0xd80): undefined reference to `mycalloc' afumfeature.c:(.text+0xd9c): undefined reference to `mycalloc' afumfeature.c:(.text+0xe80): undefined reference to `mycalloc' afumfeature.c:(.text+0x11f8): undefined reference to `myfree' afumfeature.c:(.text+0x1207): undefined reference to `myfree' afumfeature.c:(.text+0x1214): undefined reference to `myfree' ../common/libmammo.a(aggregate.o): In function `aggregate': aggregate.c:(.text+0x7fa): undefined reference to `mycalloc' aggregate.c:(.text+0x81c): undefined reference to `mycalloc' aggregate.c:(.text+0x868): undefined reference to `mycalloc' ../common/libmammo.a(aggregate.o): In function `aggregate_median': aggregate.c:(.text+0xbc5): undefined reference to `mymalloc' aggregate.c:(.text+0xbfb): undefined reference to `mycalloc' aggregate.c:(.text+0xc3c): undefined reference to `mycalloc' ../common/libmammo.a(aggregate.o): In function `aggregate': aggregate.c:(.text+0x9b5): undefined reference to `myfree' ../common/libmammo.a(aggregate.o): In function `aggregate_median': aggregate.c:(.text+0xd85): undefined reference to `myfree' ../common/libmammo.a(convexpolyscan.o): In function `polyscan_coords': convexpolyscan.c:(.text+0x6f0): undefined reference to `mycalloc' convexpolyscan.c:(.text+0x75f): undefined reference to `mycalloc' convexpolyscan.c:(.text+0x7ab): undefined reference to `myfree' convexpolyscan.c:(.text+0x7b8): undefined reference to `myfree' ../common/libmammo.a(convexpolyscan.o): In function `polyscan_poly_cacheim': convexpolyscan.c:(.text+0x805): undefined reference to `mycalloc' convexpolyscan.c:(.text+0x894): undefined reference to `myfree' ../common/libmammo.a(mikesfileio.o): In function `read_segmentation_file': mikesfileio.c:(.text+0x1e9): undefined reference to `mycalloc' mikesfileio.c:(.text+0x205): undefined reference to `mycalloc' ../common/libmammo.a(optical_density.o): In function `linear_optical_density': optical_density.c:(.text+0x29e): undefined reference to `mymalloc' optical_density.c:(.text+0x342): undefined reference to `mycalloc' optical_density.c:(.text+0x383): undefined reference to `mycalloc' ../common/libmammo.a(optical_density.o): In function `log10_optical_density': optical_density.c:(.text+0x693): undefined reference to `mymalloc' optical_density.c:(.text+0x74f): undefined reference to `mycalloc' optical_density.c:(.text+0x790): undefined reference to `mycalloc' ../common/libmammo.a(optical_density.o): In function `map_with_ushort_lut': optical_density.c:(.text+0xb2e): undefined reference to `mymalloc' optical_density.c:(.text+0xb87): undefined reference to `mycalloc' optical_density.c:(.text+0xbc6): undefined reference to `mycalloc' ../common/libmammo.a(optical_density.o): In function `linear_optical_density': optical_density.c:(.text+0x4d9): undefined reference to `myfree' ../common/libmammo.a(optical_density.o): In function `log10_optical_density': optical_density.c:(.text+0x8f1): undefined reference to `myfree' ../common/libmammo.a(optical_density.o): In function `map_with_ushort_lut': optical_density.c:(.text+0xd0d): undefined reference to `myfree' ../common/libmammo.a(virtual_image.o): In function `deallocate_cached_image': virtual_image.c:(.text+0x3dc6): undefined reference to `myfree' virtual_image.c:(.text+0x3dd7): undefined reference to `myfree' ../common/libmammo.a(virtual_image.o):virtual_image.c:(.text+0x3de5): more undefined references to `myfree' follow ../common/libmammo.a(virtual_image.o): In function `allocate_cached_image': virtual_image.c:(.text+0x4233): undefined reference to `mycalloc' virtual_image.c:(.text+0x4253): undefined reference to `mymalloc' virtual_image.c:(.text+0x4275): undefined reference to `mycalloc' virtual_image.c:(.text+0x42e7): undefined reference to `mycalloc' virtual_image.c:(.text+0x44f9): undefined reference to `mycalloc' virtual_image.c:(.text+0x47a9): undefined reference to `mycalloc' virtual_image.c:(.text+0x4a45): undefined reference to `mycalloc' virtual_image.c:(.text+0x4af4): undefined reference to `myfree' collect2: error: ld returned 1 exit status make: *** [afumfeature] Error 1 Building the mass detection program. make: Nothing to be done for `all'. Building the performance evaluation program. gcc -O2 -I. -I../common DDSMeval.o polyscan.o -o DDSMeval -L../common -lmammo -lm ../common/libmammo.a(mikesfileio.o): In function `read_segmentation_file': mikesfileio.c:(.text+0x1e9): undefined reference to `mycalloc' mikesfileio.c:(.text+0x205): undefined reference to `mycalloc' collect2: error: ld returned 1 exit status make: *** [DDSMeval] Error 1 Building the template creation program. gcc -O2 -I. -I../common mktemplate.o polyscan.o -o mktemplate -L../common -lmammo -lm Building the drawimage program. gcc -O2 -I. -I../common drawimage.o -o drawimage -L../common -lmammo -lm ../common/libmammo.a(mikesfileio.o): In function `read_segmentation_file': mikesfileio.c:(.text+0x1e9): undefined reference to `mycalloc' mikesfileio.c:(.text+0x205): undefined reference to `mycalloc' collect2: error: ld returned 1 exit status make: *** [drawimage] Error 1 Building the compression/decompression program jpeg. gcc -O2 -DSYSV -DNOTRUNCATE -c lexer.c lexer.c:41:1: error: initializer element is not constant lexer.c:41:1: error: (near initialization for ‘yyin’) lexer.c:41:1: error: initializer element is not constant lexer.c:41:1: error: (near initialization for ‘yyout’) lexer.c: In function ‘initparser’: lexer.c:387:21: warning: incompatible implicit declaration of built-in function ‘strlen’ [enabled by default] lexer.c: In function ‘MakeLink’: lexer.c:443:16: warning: incompatible implicit declaration of built-in function ‘malloc’ [enabled by default] lexer.c:447:7: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default] lexer.c:452:7: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default] lexer.c:455:34: warning: incompatible implicit declaration of built-in function ‘calloc’ [enabled by default] lexer.c:458:7: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default] lexer.c:460:3: warning: incompatible implicit declaration of built-in function ‘strcpy’ [enabled by default] lexer.c: In function ‘getstr’: lexer.c:548:26: warning: incompatible implicit declaration of built-in function ‘malloc’ [enabled by default] lexer.c:552:4: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default] lexer.c:557:21: warning: incompatible implicit declaration of built-in function ‘calloc’ [enabled by default] lexer.c:557:28: warning: incompatible implicit declaration of built-in function ‘strlen’ [enabled by default] lexer.c:561:7: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default] lexer.c: In function ‘parser’: lexer.c:794:21: warning: incompatible implicit declaration of built-in function ‘calloc’ [enabled by default] lexer.c:798:8: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default] lexer.c:1074:21: warning: incompatible implicit declaration of built-in function ‘calloc’ [enabled by default] lexer.c:1078:8: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default] lexer.c:1116:21: warning: incompatible implicit declaration of built-in function ‘calloc’ [enabled by default] lexer.c:1120:8: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default] lexer.c:1154:25: warning: incompatible implicit declaration of built-in function ‘calloc’ [enabled by default] lexer.c:1158:5: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default] lexer.c:1190:5: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default] lexer.c:1247:25: warning: incompatible implicit declaration of built-in function ‘calloc’ [enabled by default] lexer.c:1251:5: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default] lexer.c:1283:5: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default] lexer.c: In function ‘yylook’: lexer.c:1867:9: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast] lexer.c:1867:20: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast] lexer.c:1877:12: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast] lexer.c:1877:23: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast] make: *** [lexer.o] Error 1

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• Force external function to be const

  - by vanna

  Here is my problem. I made a class with a member function declared as const that uses an external function that I cannot modify (declared in someone else's code) and that is not declared const. More precisely Someone else's code class B { public: void foo(); }; My code class A : public B { public: void bar() const { this->foo(); } }; I know that for member data we can force const-correctness by using mutable or const_cast. How can I 'hack' foo such that my compiler understands that I would like to use it as if it was const even if it is not declared in someone else's code ?

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• what is the difference between const int*, const int * const, int const *

  - by ultraman

  I always mess up how to use it correctly. Is there a set of rules defining what you can and cannot do? I want to know all the Do's and all DoNOTs in terms of assignments, passing to the functions, etc. Thanks

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• Modifying a const through a non-const pointer

  - by jasonline

  I'm a bit confused what happened in the following code: const int e = 2; int* w = ( int* ) &e; // (1) cast to remove const-ness *w = 5; // (2) cout << *w << endl; // (3) outputs 5 cout << e << endl; // (4) outputs 2 cout << "w = " << w << endl; // (5) w points to the address of e cout << "&e = " << &e << endl; In (1), w points to the address of e. In (2), that value was changed to 5. However, when the values of *w and e were displayed, their values are different. But if you print value of w pointer and &e, they have the same value/address. How come e still contained 2, even if it was changed to 5? Were they stored in a separate location? Or a temporary? But how come the value pointed by w is still the address of e?

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• C++: get const or non-const reference type from trait

  - by maciekp

  I am writing a functor F which takes function of type void (*func)(T) and func's argument arg. Then functor F calls func with arg. I would like F not to copy arg, just to pass it as reference. But then I cannot simply write "void F(void (*func)(T), T&)" because T could be a reference. So I am trying to write a trait, which allows to get proper reference type of T: T -> T& T& -> T& const T -> const T& const T& -> const T& I come up with something like this: template<typename T> struct type_op { typedef T& valid_ref_type; }; template<typename T> struct type_op<T&> { typedef typename type_op<T>::valid_ref_type valid_ref_type; }; template<typename T> struct type_op<const T> { typedef const T& valid_ref_type; }; template<typename T> struct type_op<const T&> { typedef const T& valid_ref_type; }; Which doesn't work for example for void a(int x) { std::cout << x << std::endl; } F(&a, 7); Giving error: invalid initialization of non-const reference of type ‘int&’ from a temporary of type ‘int’ in passing argument 2 of ‘void f(void (*)(T), typename type_op::valid_ref_type) [with T = int]’ How to get this trait to work?

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• return value (not a reference) from the function, bound to a const reference in the calling function

  - by brainydexter

  "If you return a value (not a reference) from the function, then bind it to a const reference in the calling function, its lifetime would be extended to the scope of the calling function." So: const BoundingBox Player::GetBoundingBox(void) { return BoundingBox( &GetBoundingSphere() ); } Returns a value of type const BoundingBox from function GetBoundingBox() Called function: (From within function Update() the following is called:) variant I: (Bind it to a const reference) const BoundingBox& l_Bbox = l_pPlayer->GetBoundingBox(); variant II: (Bind it to a const copy) const BoundingBox l_Bbox = l_pPlayer->GetBoundingBox(); Both work fine and I don't see the l_Bbox object going out of scope. (Though, I understand in variant one, the copy constructor is not called and thus is slightly better than variant II). Also, for comparison, I made the following changes. BoundingBox Player::GetBoundingBox(void) { return BoundingBox( &GetBoundingSphere() ); } with Variants: I BoundingBox& l_Bbox = l_pPlayer->GetBoundingBox(); and II: BoundingBox l_Bbox = l_pPlayer->GetBoundingBox(); The objet l_Bbox still does not out scope. So, I don't see how "bind it to a const reference in the calling function, its lifetime would be extended to the scope of the calling function", really extends the lifetime of the object to the scope of the calling function ? Am I missing something trivial here..please explain .. Thanks a lot

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• Cannot initialize non-const reference from convertible type

  - by Julien L.

  Hi, I cannot initialize a non-const reference to type T1 from a convertible type T2. However, I can with a const reference. long l; const long long &const_ref = l; // fine long long &ref = l; // error: invalid initialization of reference of // type 'long long int&' from expression of type // 'long int' Most problems I encountered were related to r-values that cannot be assigned to a non-const reference. This is not the case here -- can someone explain? Thanks.

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• Double pointer const-correctness warnings in C

  - by Michael Koval

  You can obviously cast a pointer to non-const data to a a pointer of the same type to const data: int *x = NULL; int const *y = x; Adding additional const qualifiers to match the additional indirection should logically work the same way: int * *x = NULL; int *const *y = x; /* okay */ int const *const *z = y; /* warning */ Compiling this with GCC or Clang with the -Wall flag, however, results in the following warning: test.c:4:23: warning: initializing 'int const *const *' with an expression of type 'int *const *' discards qualifiers in nested pointer types int const *const *z = y; /* warning */ ^ ~ Why does adding an additional const qualifier "discard qualifiers in nested pointer types"?

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• Modifying reference member from const member function in C++

  - by Philipp

  I am working on const-correctness of my code and just wondered why this code compiles: class X { int x; int& y; public: X(int& _y):y(_y) { } void f(int& newY) const { //x = 3; would not work, that's fine y = newY; //does compile. Why? } }; int main(int argc, char **argv) { int i1=0, i2=0; X myX(i1); myX.f(i2); ... } As far as I understand, f() is changing the object myX, although it says to be const. How can I ensure my compiler complains when I do assign to y? (Visual C++ 2008) Thank a lot!

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• What is the best Broadphase Interface for moving spheres?

  - by Molmasepic

  As of now I am working on optimizing the performance of the physics and collision, and as of now I am having some slowdowns on my other computers from my main. I have well over 3000 btSphereShape Rigidbodies and 2/3 of them do not move at all, but I am noticing(by the profile below) that collision is taking a bit of time to maneuver. Each sample counts as 0.01 seconds. % cumulative self self total time seconds seconds calls ms/call ms/call name 10.09 0.65 0.65 SphereTriangleDetector::collide(btVector3 const&, btVector3&, btVector3&, float&, float&, float) 7.61 1.14 0.49 btSphereTriangleCollisionAlgorithm::processCollision(btCollisionObject*, btCollisionObject*, btDispatcherInfo const&, btManifoldResult*) 5.59 1.50 0.36 btConvexTriangleCallback::processTriangle(btVector3*, int, int) 5.43 1.85 0.35 btQuantizedBvh::reportAabbOverlappingNodex(btNodeOverlapCallback*, btVector3 const&, btVector3 const&) const 4.97 2.17 0.32 btBvhTriangleMeshShape::processAllTriangles(btTriangleCallback*, btVector3 const&, btVector3 const&) const::MyNodeOverlapCallback::processNode(int, int) 4.19 2.44 0.27 btSequentialImpulseConstraintSolver::resolveSingleConstraintRowGeneric(btRigidBody&, btRigidBody&, btSolverConstraint const&) 4.04 2.70 0.26 btSequentialImpulseConstraintSolver::resolveSingleConstraintRowLowerLimit(btRigidBody&, btRigidBody&, btSolverConstraint const&) 3.73 2.94 0.24 Ogre::OctreeSceneManager::walkOctree(Ogre::OctreeCamera*, Ogre::RenderQueue*, Ogre::Octree*, Ogre::VisibleObjectsBoundsInfo*, bool, bool) 3.42 3.16 0.22 btTriangleShape::getVertex(int, btVector3&) const 2.48 3.32 0.16 Ogre::Frustum::isVisible(Ogre::AxisAlignedBox const&, Ogre::FrustumPlane*) const 2.33 3.47 0.15 1246357 0.00 0.00 Gorilla::Layer::setVisible(bool) 2.33 3.62 0.15 SphereTriangleDetector::getClosestPoints(btDiscreteCollisionDetectorInterface::ClosestPointInput const&, btDiscreteCollisionDetectorInterface::Result&, btIDebugDraw*, bool) 1.86 3.74 0.12 btCollisionDispatcher::findAlgorithm(btCollisionObject*, btCollisionObject*, btPersistentManifold*) 1.86 3.86 0.12 btSequentialImpulseConstraintSolver::setupContactConstraint(btSolverConstraint&, btCollisionObject*, btCollisionObject*, btManifoldPoint&, btContactSolverInfo const&, btVector3&, float&, float&, btVector3&, btVector3&) 1.71 3.97 0.11 btTriangleShape::getEdge(int, btVector3&, btVector3&) const 1.55 4.07 0.10 _Unwind_SjLj_Register 1.55 4.17 0.10 _Unwind_SjLj_Unregister 1.55 4.27 0.10 Ogre::D3D9HardwareVertexBuffer::updateBufferResources(char const*, Ogre::D3D9HardwareVertexBuffer::BufferResources*) 1.40 4.36 0.09 btManifoldResult::addContactPoint(btVector3 const&, btVector3 const&, float) 1.40 4.45 0.09 btSequentialImpulseConstraintSolver::setupFrictionConstraint(btSolverConstraint&, btVector3 const&, btRigidBody*, btRigidBody*, btManifoldPoint&, btVector3 const&, btVector3 const&, btCollisionObject*, btCollisionObject*, float, float, float) 1.24 4.53 0.08 btSequentialImpulseConstraintSolver::convertContact(btPersistentManifold*, btContactSolverInfo const&) 1.09 4.60 0.07 408760 0.00 0.00 Living::MapHide() 1.09 4.67 0.07 btSphereTriangleCollisionAlgorithm::~btSphereTriangleCollisionAlgorithm() 1.09 4.74 0.07 inflate_fast EDIT: Updated to show current Profile. I have only listed the functions using over 1% time from the many functions that are being used. Another thing is that each monster has a certain area that they stay in and are only active when a player is in said area. I was wondering if maybe there is a way to deactivate the non-active monsters from bullet(reactivating once in the area again) or maybe theres a different broadphase interface that I should use. The current BPI is btDbvtBroadphase. EDIT: Here is the Profile on the other computer(the top one is my main) Each sample counts as 0.01 seconds. % cumulative self self total time seconds seconds calls ms/call ms/call name 12.18 1.19 1.19 SphereTriangleDetector::collide(btVector3 const&, btVector3&, btVector3&, float&, float&, float) 6.76 1.85 0.66 btSphereTriangleCollisionAlgorithm::processCollision(btCollisionObject*, btCollisionObject*, btDispatcherInfo const&, btManifoldResult*) 5.83 2.42 0.57 btQuantizedBvh::reportAabbOverlappingNodex(btNodeOverlapCallback*, btVector3 const&, btVector3 const&) const 5.12 2.92 0.50 btConvexTriangleCallback::processTriangle(btVector3*, int, int) 4.61 3.37 0.45 btTriangleShape::getVertex(int, btVector3&) const 4.09 3.77 0.40 _Unwind_SjLj_Register 3.48 4.11 0.34 btBvhTriangleMeshShape::processAllTriangles(btTriangleCallback*, btVector3 const&, btVector3 const&) const::MyNodeOverlapCallback::processNode(int, int) 2.46 4.35 0.24 btSequentialImpulseConstraintSolver::resolveSingleConstraintRowLowerLimit(btRigidBody&, btRigidBody&, btSolverConstraint const&) 2.15 4.56 0.21 _Unwind_SjLj_Unregister 2.15 4.77 0.21 SphereTriangleDetector::getClosestPoints(btDiscreteCollisionDetectorInterface::ClosestPointInput const&, btDiscreteCollisionDetectorInterface::Result&, btIDebugDraw*, bool) 1.84 4.95 0.18 btTriangleShape::getEdge(int, btVector3&, btVector3&) const 1.64 5.11 0.16 btSequentialImpulseConstraintSolver::resolveSingleConstraintRowGeneric(btRigidBody&, btRigidBody&, btSolverConstraint const&) 1.54 5.26 0.15 btSequentialImpulseConstraintSolver::setupContactConstraint(btSolverConstraint&, btCollisionObject*, btCollisionObject*, btManifoldPoint&, btContactSolverInfo const&, btVector3&, float&, float&, btVector3&, btVector3&) 1.43 5.40 0.14 Ogre::D3D9HardwareVertexBuffer::updateBufferResources(char const*, Ogre::D3D9HardwareVertexBuffer::BufferResources*) 1.33 5.53 0.13 btManifoldResult::addContactPoint(btVector3 const&, btVector3 const&, float) 1.13 5.64 0.11 btRigidBody::predictIntegratedTransform(float, btTransform&) 1.13 5.75 0.11 btTriangleIndexVertexArray::getLockedReadOnlyVertexIndexBase(unsigned char const**, int&, PHY_ScalarType&, int&, unsigned char const**, int&, int&, PHY_ScalarType&, int) const 1.02 5.85 0.10 btSphereTriangleCollisionAlgorithm::CreateFunc::CreateCollisionAlgorithm(btCollisionAlgorithmConstructionInfo&, btCollisionObject*, btCollisionObject*) 1.02 5.95 0.10 btSphereTriangleCollisionAlgorithm::btSphereTriangleCollisionAlgorithm(btPersistentManifold*, btCollisionAlgorithmConstructionInfo const&, btCollisionObject*, btCollisionObject*, bool) Edited same as other Profile.

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• Qt Linking Error.

  - by Wallah

  Hi, I configure qt-x11 with following options ./configure -prefix /iTalk/qtx11 -prefix-install -bindir /iTalk/qtx11-install/bin -libdir /iTalk/qtx11-install/lib -docdir /iTalk/qtx11-install/doc -headerdir /iTalk/qtx11-install/include -datadir /iTalk/qtx11-install/data -examplesdir /iTalk/qtx11-install/examples -demosdir /iTalk/qtx11-install/demos -debug. Now I am getting following errors in Fedora Core 6. Can you please tell me where the problem is? obj/debug-shared/qapplication_x11.o: In function `qt_init(QApplicationPrivate*, int, _XDisplay*, unsigned long, unsigned long)': /iTalk/QT4/qt/src/gui/kernel/qapplication_x11.cpp:1713: undefined reference to `FcInit' .obj/debug-shared/qfontdatabase.o: In function `queryFont': /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1727: undefined reference to `FcFreeTypeQuery' .obj/debug-shared/qfontdatabase.o: In function `registerFont': /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1959: undefined reference to `FcConfigGetCurrent' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1963: undefined reference to `FcConfigGetFonts' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1965: undefined reference to `FcConfigAppFontAddFile' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1966: undefined reference to `FcConfigGetFonts' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1985: undefined reference to `FcConfigGetBlanks' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1997: undefined reference to `FcPatternDel' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1998: undefined reference to `FcPatternAddString' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:2001: undefined reference to `FcPatternGetString' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:2006: undefined reference to `FcFontSetAdd' .obj/debug-shared/qfontdatabase.o: In function `qt_FcPatternToQFontDef(_FcPattern*, QFontDef const&)': /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:746: undefined reference to `FcPatternGetString' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:751: undefined reference to `FcPatternGetDouble' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:759: undefined reference to `FcPatternGetDouble' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:771: undefined reference to `FcPatternGetInteger' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:776: undefined reference to `FcPatternGetInteger' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:786: undefined reference to `FcPatternGetBool' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:793: undefined reference to `FcPatternGetInteger' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:800: undefined reference to `FcPatternGetInteger' .obj/debug-shared/qfontdatabase.o: In function `FcFontSetRemove': /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1573: undefined reference to `FcPatternDestroy' .obj/debug-shared/qfontdatabase.o: In function `qt_fontSetForPattern(_FcPattern*, QFontDef const&)': /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1657: undefined reference to `FcFontSort' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1671: undefined reference to `FcPatternGetBool' .obj/debug-shared/qfontdatabase.o: In function `qt_addPatternProps(_FcPattern*, int, int, QFontDef const&)': /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1449: undefined reference to `FcPatternAddInteger' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1456: undefined reference to `FcPatternAddInteger' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1459: undefined reference to `FcPatternAddDouble' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1464: undefined reference to `FcPatternAddInteger' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1468: undefined reference to `FcPatternAddBool' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1471: undefined reference to `FcPatternAddBool' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1476: undefined reference to `FcLangSetCreate' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1477: undefined reference to `FcLangSetAdd' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1478: undefined reference to `FcPatternAddLangSet' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1479: undefined reference to `FcLangSetDestroy' .obj/debug-shared/qfontdatabase.o: In function `tryPatternLoad': /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1588: undefined reference to `FcPatternDuplicate' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1593: undefined reference to `FcConfigSubstitute' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1594: undefined reference to `FcDefaultSubstitute' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1596: undefined reference to `FcFontMatch' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1606: undefined reference to `FcPatternDuplicate' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1613: undefined reference to `FcPatternGetCharSet' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1615: undefined reference to `FcCharSetHasChar' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1619: undefined reference to `FcPatternGetLangSet' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1621: undefined reference to `FcLangSetHasLang' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1628: undefined reference to `FcPatternDel' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1629: undefined reference to `FcPatternAddBool' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1646: undefined reference to `FcPatternDestroy' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1648: undefined reference to `FcPatternDestroy' .obj/debug-shared/qfontdatabase.o: In function `loadFontConfig': /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1023: undefined reference to `FcObjectSetCreate' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1024: undefined reference to `FcPatternCreate' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1037: undefined reference to `FcObjectSetAdd' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1040: undefined reference to `FcFontList' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1041: undefined reference to `FcObjectSetDestroy' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1042: undefined reference to `FcPatternDestroy' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1046: undefined reference to `FcPatternGetString' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1057: undefined reference to `FcPatternGetInteger' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1059: undefined reference to `FcPatternGetInteger' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1061: undefined reference to `FcPatternGetInteger' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1063: undefined reference to `FcPatternGetString' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1065: undefined reference to `FcPatternGetInteger' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1067: undefined reference to `FcPatternGetBool' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1069: undefined reference to `FcPatternGetString' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1074: undefined reference to `FcPatternGetLangSet' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1081: undefined reference to `FcLangSetHasLang' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1100: undefined reference to `FcPatternGetCharSet' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1107: undefined reference to `FcCharSetHasChar' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1116: undefined reference to `FcPatternGetString' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1136: undefined reference to `FcPatternGetInteger' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1153: undefined reference to `FcPatternGetDouble' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1161: undefined reference to `FcFontSetDestroy' .obj/debug-shared/qfontdatabase.o: In function `getFcPattern': /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1494: undefined reference to `FcPatternCreate' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1509: undefined reference to `FcPatternAdd' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1516: undefined reference to `FcPatternAddWeak' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1524: undefined reference to `FcPatternAddWeak' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1531: undefined reference to `FcPatternAddInteger' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1533: undefined reference to `FcPatternAddBool' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1535: undefined reference to `FcPatternAddBool' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1539: undefined reference to `FcDefaultSubstitute' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1540: undefined reference to `FcConfigSubstitute' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1541: undefined reference to `FcConfigSubstitute' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1550: undefined reference to `FcPatternAddWeak' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1557: undefined reference to `FcPatternAddWeak' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1564: undefined reference to `FcPatternAddWeak' .obj/debug-shared/qfontdatabase.o: In function `loadFc': /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1707: undefined reference to `FcFontSetDestroy' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1716: undefined reference to `FcPatternDestroy' /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:1718: undefined reference to `FcPatternDestroy' .obj/debug-shared/qfontdatabase.o: In function `QFontDatabase::removeAllApplicationFonts()': /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:2048: undefined reference to `FcConfigAppFontClear' .obj/debug-shared/qfontdatabase.o: In function `QFontDatabase::removeApplicationFont(int)': /iTalk/QT4/qt/src/gui/text/qfontdatabase_x11.cpp:2027: undefined reference to `FcConfigAppFontClear' .obj/debug-shared/qfontengine_x11.o: In function `qt_x11ft_convert_pattern(_FcPattern*, QByteArray*, int*, bool*)': /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:970: undefined reference to `FcPatternGetString' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:972: undefined reference to `FcPatternGetInteger' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:975: undefined reference to `FcPatternGetBool' .obj/debug-shared/qfontengine_x11.o: In function `QFontEngineX11FT': /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:999: undefined reference to `FcPatternGetInteger' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:1016: undefined reference to `FcPatternGetInteger' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:1041: undefined reference to `FcPatternGetBool' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:1077: undefined reference to `FcPatternGetBool' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:1106: undefined reference to `FcPatternDestroy' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:1112: undefined reference to `FcPatternGetCharSet' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:1113: undefined reference to `FcCharSetCopy' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:1115: undefined reference to `FcPatternDestroy' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:999: undefined reference to `FcPatternGetInteger' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:1016: undefined reference to `FcPatternGetInteger' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:1041: undefined reference to `FcPatternGetBool' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:1077: undefined reference to `FcPatternGetBool' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:1106: undefined reference to `FcPatternDestroy' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:1112: undefined reference to `FcPatternGetCharSet' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:1113: undefined reference to `FcCharSetCopy' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:1115: undefined reference to `FcPatternDestroy' .obj/debug-shared/qfontengine_x11.o: In function `engineForPattern': /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:868: undefined reference to `FcFontMatch' .obj/debug-shared/qfontengine_x11.o: In function `QFontEngineMultiFT::loadEngine(int)': /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:929: undefined reference to `FcPatternEqual' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:932: undefined reference to `FcPatternDestroy' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:941: undefined reference to `FcPatternDuplicate' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:951: undefined reference to `FcConfigSubstitute' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:952: undefined reference to `FcDefaultSubstitute' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:956: undefined reference to `FcPatternDestroy' .obj/debug-shared/qfontengine_x11.o: In function `~QFontEngineMultiFT': /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:895: undefined reference to `FcPatternDestroy' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:897: undefined reference to `FcPatternDestroy' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:899: undefined reference to `FcFontSetDestroy' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:895: undefined reference to `FcPatternDestroy' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:897: undefined reference to `FcPatternDestroy' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:899: undefined reference to `FcFontSetDestroy' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:895: undefined reference to `FcPatternDestroy' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:897: undefined reference to `FcPatternDestroy' /iTalk/QT4/qt/src/gui/text/qfontengine_x11.cpp:899: undefined reference to `FcFontSetDestroy' .obj/debug-shared/qfontengine_ft.o: In function `QFontEngineFT::stringToCMap(QChar const*, int, QGlyphLayout*, int*, QFlags) const': /iTalk/QT4/qt/src/gui/text/qfontengine_ft.cpp:1546: undefined reference to `FcCharSetHasChar' /iTalk/QT4/qt/src/gui/text/qfontengine_ft.cpp:1581: undefined reference to `FcCharSetHasChar' .obj/debug-shared/qfontengine_ft.o: In function `QFreetypeFace::release(QFontEngine::FaceId const&)': /iTalk/QT4/qt/src/gui/text/qfontengine_ft.cpp:308: undefined reference to `FcCharSetDestroy' collect2: ld returned 1 exit status make[1]: *** [../../lib/libQtGui.so.4.5.3] Error 1 make[1]: Leaving directory `/iTalk/QT4/qt/src/gui' make: *** [sub-gui-make_default-ordered] Error 2

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• Difference between const reference and normal parameter

  - by Pirate for Profit

  void DoWork(int n); void DoWork(const int &n); Whats the diff

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• Template inheritence c++

  - by Chris Condy

  I have made a template singleton class, I have also made a data structure that is templated. My question is; how do I make my templated data structure inherit from a singleton so you can only have one float type of this structure? I have tested both seperate and have found no problems. Code provided under... (That is the problem) template <class Type> class AbstractRManagers : public Singleton<AbstractRManagers<Type> > The problem is the code above doesn't work I get alot of errors. I cant get it to no matter what I do template a templated singleton class... I was asking for maybe advice or maybe if the code above is incorrect guidence? #ifndef SINGLETON_H #define SINGLETON_H template <class Type> class Singleton { public: virtual ~Singleton(); Singleton(); static Type* m_instance; }; template <class Type> Type* Singleton<Type>::m_instance = 0; #include "Singleton.cpp" #endif #ifndef SINGLETON_CPP #define SINGLETON_CPP #include "Singleton.h" template <class Type> Singleton<Type>::Singleton() { } template <class Type> Singleton<Type>::~Singleton() { } template <class Type> Type* Singleton<Type>::getInstance() { if(m_instance==nullptr) { m_instance = new Type; } return m_instance; } #endif #ifndef ABSTRACTRMANAGERS_H #define ABSTRACTRMANAGERS_H #include <vector> #include <map> #include <stack> #include "Singleton.h" template <class Type> class AbstractRManagers : public Singleton<AbstractRManagers<Type> > { public: virtual ~AbstractRManagers(); int insert(Type* type, std::string name); Type* remove(int i); Type* remove(std::string name); Type* get(int i); Type* getS(std::string name); int get(std::string name); int get(Type* i); bool check(std::string name); int resourceSize(); protected: private: std::vector<Type*> m_resources; std::map<std::string,int> m_map; std::stack<int> m_freePos; }; #include "AbstractRManagers.cpp" #endif #ifndef ABSTRACTRMANAGERS_CPP #define ABSTRACTRMANAGERS_CPP #include "AbstractRManagers.h" template <class Type> int AbstractRManagers<Type>::insert(Type* type, std::string name) { int i=0; if(!check(name)) { if(m_freePos.empty()) { m_resources.push_back(type); i = m_resources.size()-1; m_map[name] = i; } else { i = m_freePos.top(); m_freePos.pop(); m_resources[i] = type; m_map[name] = i; } } else i = -1; return i; } template <class Type> int AbstractRManagers<Type>::resourceSize() { return m_resources.size(); } template <class Type> bool AbstractRManagers<Type>::check(std::string name) { std::map<std::string,int>::iterator it; it = m_map.find(name); if(it==m_map.end()) return false; return true; } template <class Type> Type* AbstractRManagers<Type>::remove(std::string name) { Type* temp = m_resources[m_map[name]]; if(temp!=NULL) { std::map<std::string,int>::iterator it; it = m_map[name]; m_resources[m_map[name]] = NULL; m_freePos.push(m_map[name]); delete (*it).second; delete (*it).first; return temp; } return NULL; } template <class Type> Type* AbstractRManagers<Type>::remove(int i) { if((i < m_resources.size())&&(i > 0)) { Type* temp = m_resources[i]; m_resources[i] = NULL; m_freePos.push(i); std::map<std::string,int>::iterator it; for(it=m_map.begin();it!=m_map.end();it++) { if((*it).second == i) { delete (*it).second; delete (*it).first; return temp; } } return temp; } return NULL; } template <class Type> int AbstractRManagers<Type>::get(Type* i) { for(int i2=0;i2<m_resources.size();i2++) { if(i == m_resources[i2]) { return i2; } } return -1; } template <class Type> Type* AbstractRManagers<Type>::get(int i) { if((i < m_resources.size())&&(i >= 0)) { return m_resources[i]; } return NULL; } template <class Type> Type* AbstractRManagers<Type>::getS(std::string name) { return m_resources[m_map[name]]; } template <class Type> int AbstractRManagers<Type>::get(std::string name) { return m_map[name]; } template <class Type> AbstractRManagers<Type>::~AbstractRManagers() { } #endif #include "AbstractRManagers.h" struct b { float x; }; int main() { b* a = new b(); AbstractRManagers<b>::getInstance()->insert(a,"a"); return 0; } This program produces next errors when compiled : 1> main.cpp 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::stack<_Ty,_Container> &,const std::stack<_Ty,_Container> &)' : could not deduce template argument for 'const std::stack<_Ty,_Container> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\stack(166) : see declaration of 'std::operator <' 1> c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(124) : while compiling class template member function 'bool std::less<_Ty>::operator ()(const _Ty &,const _Ty &) const' 1> with 1> [ 1> _Ty=std::string 1> ] 1> c:\program files\microsoft visual studio 10.0\vc\include\map(71) : see reference to class template instantiation 'std::less<_Ty>' being compiled 1> with 1> [ 1> _Ty=std::string 1> ] 1> c:\program files\microsoft visual studio 10.0\vc\include\xtree(451) : see reference to class template instantiation 'std::_Tmap_traits<_Kty,_Ty,_Pr,_Alloc,_Mfl>' being compiled 1> with 1> [ 1> _Kty=std::string, 1> _Ty=int, 1> _Pr=std::less<std::string>, 1> _Alloc=std::allocator<std::pair<const std::string,int>>, 1> _Mfl=false 1> ] 1> c:\program files\microsoft visual studio 10.0\vc\include\xtree(520) : see reference to class template instantiation 'std::_Tree_nod<_Traits>' being compiled 1> with 1> [ 1> _Traits=std::_Tmap_traits<std::string,int,std::less<std::string>,std::allocator<std::pair<const std::string,int>>,false> 1> ] 1> c:\program files\microsoft visual studio 10.0\vc\include\xtree(659) : see reference to class template instantiation 'std::_Tree_val<_Traits>' being compiled 1> with 1> [ 1> _Traits=std::_Tmap_traits<std::string,int,std::less<std::string>,std::allocator<std::pair<const std::string,int>>,false> 1> ] 1> c:\program files\microsoft visual studio 10.0\vc\include\map(81) : see reference to class template instantiation 'std::_Tree<_Traits>' being compiled 1> with 1> [ 1> _Traits=std::_Tmap_traits<std::string,int,std::less<std::string>,std::allocator<std::pair<const std::string,int>>,false> 1> ] 1> c:\users\chris\desktop\311\ideas\idea1\idea1\abstractrmanagers.h(28) : see reference to class template instantiation 'std::map<_Kty,_Ty>' being compiled 1> with 1> [ 1> _Kty=std::string, 1> _Ty=int 1> ] 1> c:\users\chris\desktop\311\ideas\idea1\idea1\abstractrmanagers.h(30) : see reference to class template instantiation 'AbstractRManagers<Type>' being compiled 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::stack<_Ty,_Container> &,const std::stack<_Ty,_Container> &)' : could not deduce template argument for 'const std::stack<_Ty,_Container> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\stack(166) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::stack<_Ty,_Container> &,const std::stack<_Ty,_Container> &)' : could not deduce template argument for 'const std::stack<_Ty,_Container> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\stack(166) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::deque<_Ty,_Alloc> &,const std::deque<_Ty,_Alloc> &)' : could not deduce template argument for 'const std::deque<_Ty,_Alloc> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\deque(1725) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::deque<_Ty,_Alloc> &,const std::deque<_Ty,_Alloc> &)' : could not deduce template argument for 'const std::deque<_Ty,_Alloc> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\deque(1725) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::deque<_Ty,_Alloc> &,const std::deque<_Ty,_Alloc> &)' : could not deduce template argument for 'const std::deque<_Ty,_Alloc> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\deque(1725) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::_Tree<_Traits> &,const std::_Tree<_Traits> &)' : could not deduce template argument for 'const std::_Tree<_Traits> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xtree(1885) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::_Tree<_Traits> &,const std::_Tree<_Traits> &)' : could not deduce template argument for 'const std::_Tree<_Traits> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xtree(1885) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::_Tree<_Traits> &,const std::_Tree<_Traits> &)' : could not deduce template argument for 'const std::_Tree<_Traits> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xtree(1885) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::vector<_Ty,_Ax> &,const std::vector<_Ty,_Ax> &)' : could not deduce template argument for 'const std::vector<_Ty,_Ax> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\vector(1502) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::vector<_Ty,_Ax> &,const std::vector<_Ty,_Ax> &)' : could not deduce template argument for 'const std::vector<_Ty,_Ax> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\vector(1502) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::vector<_Ty,_Ax> &,const std::vector<_Ty,_Ax> &)' : could not deduce template argument for 'const std::vector<_Ty,_Ax> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\vector(1502) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::unique_ptr<_Ty,_Dx> &,const std::unique_ptr<_Ty2,_Dx2> &)' : could not deduce template argument for 'const std::unique_ptr<_Ty,_Dx> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\memory(2582) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::unique_ptr<_Ty,_Dx> &,const std::unique_ptr<_Ty2,_Dx2> &)' : could not deduce template argument for 'const std::unique_ptr<_Ty,_Dx> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\memory(2582) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::unique_ptr<_Ty,_Dx> &,const std::unique_ptr<_Ty2,_Dx2> &)' : could not deduce template argument for 'const std::unique_ptr<_Ty,_Dx> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\memory(2582) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::reverse_iterator<_RanIt> &,const std::reverse_iterator<_RanIt2> &)' : could not deduce template argument for 'const std::reverse_iterator<_RanIt> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(1356) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::reverse_iterator<_RanIt> &,const std::reverse_iterator<_RanIt2> &)' : could not deduce template argument for 'const std::reverse_iterator<_RanIt> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(1356) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::reverse_iterator<_RanIt> &,const std::reverse_iterator<_RanIt2> &)' : could not deduce template argument for 'const std::reverse_iterator<_RanIt> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(1356) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::_Revranit<_RanIt,_Base> &,const std::_Revranit<_RanIt2,_Base2> &)' : could not deduce template argument for 'const std::_Revranit<_RanIt,_Base> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(1179) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::_Revranit<_RanIt,_Base> &,const std::_Revranit<_RanIt2,_Base2> &)' : could not deduce template argument for 'const std::_Revranit<_RanIt,_Base> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(1179) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::_Revranit<_RanIt,_Base> &,const std::_Revranit<_RanIt2,_Base2> &)' : could not deduce template argument for 'const std::_Revranit<_RanIt,_Base> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(1179) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::pair<_Ty1,_Ty2> &,const std::pair<_Ty1,_Ty2> &)' : could not deduce template argument for 'const std::pair<_Ty1,_Ty2> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\utility(318) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::pair<_Ty1,_Ty2> &,const std::pair<_Ty1,_Ty2> &)' : could not deduce template argument for 'const std::pair<_Ty1,_Ty2> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\utility(318) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::pair<_Ty1,_Ty2> &,const std::pair<_Ty1,_Ty2> &)' : could not deduce template argument for 'const std::pair<_Ty1,_Ty2> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\utility(318) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2676: binary '<' : 'const std::string' does not define this operator or a conversion to a type acceptable to the predefined operator ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

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• C++ Passing `this` into method by reference

  - by David

  I have a class constructor that expects a reference to another class object to be passed in as an argument. I understand that references are preferable to pointers when no pointer arithmetic will be performed or when a null value will not exist. This is the header declaration of the constructor: class MixerLine { private: MIXERLINE _mixerLine; public: MixerLine(const MixerDevice& const parentMixer, DWORD destinationIndex); ~MixerLine(); } This is the code that calls the constructor (MixerDevice.cpp): void MixerDevice::enumerateLines() { DWORD numLines = getDestinationCount(); for(DWORD i=0;i<numLines;i++) { MixerLine mixerLine( this, i ); // other code here removed } } Compilation of MixerDevice.cpp fails with this error: Error 3 error C2664: 'MixerLine::MixerLine(const MixerDevice &,DWORD)' : cannot convert parameter 1 from 'MixerDevice *const ' to 'const MixerDevice &' But I thought pointer values could be assigned to pointers, e.g. Foo* foo = new Foo(); Foo& bar = foo;

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• int vs const int&

  - by Valdo

  I've noticed that I usually use constant references as return values or arguments. I think the reason is that it works almost the same as using non-reference in the code. But it definitely takes more space and function declarations become longer. I'm OK with such code but I think some people my find it a bad programming style. What do you think? Is it worth writing const int& over int? I think it's optimized by the compiler anyway, so maybe I'm just wasting my time coding it, a?

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• C++ constant reference lifetime

  - by aaa

  hello I have code that looks like this: class T {}; class container { const T &first, T &second; container(const T&first, const T & second); }; class adapter : T {}; container(adapter(), adapter()); I thought lifetime of constant reference would be lifetime of container. However, it appears otherwise, adapter object is destroyed after container is created, leading dangling reference. What is the correct lifetime? how to correctly implement binding temporary object to class member reference? Thanks

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• Does it ever make sense to make a fundamental (non-pointer) parameter const?

  - by Scott Smith

  I recently had an exchange with another C++ developer about the following use of const: void Foo(const int bar); He felt that using const in this way was good practice. I argued that it does nothing for the caller of the function (since a copy of the argument was going to be passed, there is no additional guarantee of safety with regard to overwrite). In addition, doing this prevents the implementer of Foo from modifying their private copy of the argument. So, it both mandates and advertises an implementation detail. Not the end of the world, but certainly not something to be recommended as good practice. I'm curious as to what others think on this issue. Edit: OK, I didn't realize that const-ness of the arguments didn't factor into the signature of the function. So, it is possible to mark the arguments as const in the implementation (.cpp), and not in the header (.h) - and the compiler is fine with that. That being the case, I guess the policy should be the same for making local variables const. One could make the argument that having different looking signatures in the header and source file would confuse others (as it would have confused me). While I try to follow the Principle of Least Astonishment with whatever I write, I guess it's reasonable to expect developers to recognize this as legal and useful.

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• const TypedeffedIntPointer not equal to const int *

  - by dirk

  I have the following C++ code: typedef int* IntPtr; const int* cip = new int; const IntPtr ctip4 = cip; I compile this with Visual Studio 2008 and get the following error: error C2440: 'initializing' : cannot convert from 'const int *' to 'const IntPtr' Clearly my understanding of typedefs is not what is should be. The reason I'm asking, I'm storing a pointer type in a STL map. I have a function that returns a const pointer which I would like to use to search in the map (using map::find(const key_type&). Since const MyType* and const map<MyType*, somedata>::key_type is incompatible, I'm having problems. Regards Dirk

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• const member functions can call const member functions only?

  - by Abhi

  Hi all. Do const member functions call only const member functions? class Transmitter{ const static string msg; mutable int size; public: void xmit() const{ size = compute(); cout<<msg; } private: int compute() const{return 5;} }; string const Transmitter::msg = "beep"; int main(){ Transmitter t; t.xmit(); return EXIT_SUCCESS; } If i dont make compute() a const, then the compiler complains. Is it because since a const member function is not allowed to modify members, it wont allow any calls to non-consts since it would mean that the const member function would be 'indirectly' modifying the data members?

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• Higher order function « filter » in C++

  - by Red Hyena

  Hi all. I wanted to write a higher order function filter with C++. The code I have come up with so far is as follows: #include <iostream> #include <string> #include <functional> #include <algorithm> #include <vector> #include <list> #include <iterator> using namespace std; bool isOdd(int const i) { return i % 2 != 0; } template < template <class, class> class Container, class Predicate, class Allocator, class A > Container<A, Allocator> filter(Container<A, Allocator> const & container, Predicate const & pred) { Container<A, Allocator> filtered(container); container.erase(remove_if(filtered.begin(), filtered.end(), pred), filtered.end()); return filtered; } int main() { int const a[] = {23, 12, 78, 21, 97, 64}; vector<int const> const v(a, a + 6); vector<int const> const filtered = filter(v, isOdd); copy(filtered.begin(), filtered.end(), ostream_iterator<int const>(cout, " ")); } However on compiling this code, I get the following error messages that I am unable to understand and hence get rid of: /usr/include/c++/4.3/ext/new_allocator.h: In instantiation of ‘__gnu_cxx::new_allocator<const int>’: /usr/include/c++/4.3/bits/allocator.h:84: instantiated from ‘std::allocator<const int>’ /usr/include/c++/4.3/bits/stl_vector.h:75: instantiated from ‘std::_Vector_base<const int, std::allocator<const int> >’ /usr/include/c++/4.3/bits/stl_vector.h:176: instantiated from ‘std::vector<const int, std::allocator<const int> >’ Filter.cpp:29: instantiated from here /usr/include/c++/4.3/ext/new_allocator.h:82: error: ‘const _Tp* __gnu_cxx::new_allocator<_Tp>::address(const _Tp&) const [with _Tp = const int]’ cannot be overloaded /usr/include/c++/4.3/ext/new_allocator.h:79: error: with ‘_Tp* __gnu_cxx::new_allocator<_Tp>::address(_Tp&) const [with _Tp = const int]’ Filter.cpp: In function ‘Container<A, Allocator> filter(const Container<A, Allocator>&, const Predicate&) [with Container = std::vector, Predicate = bool ()(int), Allocator = std::allocator<const int>, A = const int]’: Filter.cpp:30: instantiated from here Filter.cpp:23: error: passing ‘const std::vector<const int, std::allocator<const int> >’ as ‘this’ argument of ‘__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> > std::vector<_Tp, _Alloc>::erase(__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >, __gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >) [with _Tp = const int, _Alloc = std::allocator<const int>]’ discards qualifiers /usr/include/c++/4.3/bits/stl_algo.h: In function ‘_FIter std::remove_if(_FIter, _FIter, _Predicate) [with _FIter = __gnu_cxx::__normal_iterator<const int*, std::vector<const int, std::allocator<const int> > >, _Predicate = bool (*)(int)]’: Filter.cpp:23: instantiated from ‘Container<A, Allocator> filter(const Container<A, Allocator>&, const Predicate&) [with Container = std::vector, Predicate = bool ()(int), Allocator = std::allocator<const int>, A = const int]’ Filter.cpp:30: instantiated from here /usr/include/c++/4.3/bits/stl_algo.h:821: error: assignment of read-only location ‘__result.__gnu_cxx::__normal_iterator<_Iterator, _Container>::operator* [with _Iterator = const int*, _Container = std::vector<const int, std::allocator<const int> >]()’ /usr/include/c++/4.3/ext/new_allocator.h: In member function ‘void __gnu_cxx::new_allocator<_Tp>::deallocate(_Tp*, size_t) [with _Tp = const int]’: /usr/include/c++/4.3/bits/stl_vector.h:150: instantiated from ‘void std::_Vector_base<_Tp, _Alloc>::_M_deallocate(_Tp*, size_t) [with _Tp = const int, _Alloc = std::allocator<const int>]’ /usr/include/c++/4.3/bits/stl_vector.h:136: instantiated from ‘std::_Vector_base<_Tp, _Alloc>::~_Vector_base() [with _Tp = const int, _Alloc = std::allocator<const int>]’ /usr/include/c++/4.3/bits/stl_vector.h:286: instantiated from ‘std::vector<_Tp, _Alloc>::vector(_InputIterator, _InputIterator, const _Alloc&) [with _InputIterator = const int*, _Tp = const int, _Alloc = std::allocator<const int>]’ Filter.cpp:29: instantiated from here /usr/include/c++/4.3/ext/new_allocator.h:98: error: invalid conversion from ‘const void*’ to ‘void*’ /usr/include/c++/4.3/ext/new_allocator.h:98: error: initializing argument 1 of ‘void operator delete(void*)’ /usr/include/c++/4.3/bits/stl_algobase.h: In function ‘_OI std::__copy_move_a(_II, _II, _OI) [with bool _IsMove = false, _II = const int*, _OI = const int*]’: /usr/include/c++/4.3/bits/stl_algobase.h:435: instantiated from ‘_OI std::__copy_move_a2(_II, _II, _OI) [with bool _IsMove = false, _II = __gnu_cxx::__normal_iterator<const int*, std::vector<const int, std::allocator<const int> > >, _OI = __gnu_cxx::__normal_iterator<const int*, std::vector<const int, std::allocator<const int> > >]’ /usr/include/c++/4.3/bits/stl_algobase.h:466: instantiated from ‘_OI std::copy(_II, _II, _OI) [with _II = __gnu_cxx::__normal_iterator<const int*, std::vector<const int, std::allocator<const int> > >, _OI = __gnu_cxx::__normal_iterator<const int*, std::vector<const int, std::allocator<const int> > >]’ /usr/include/c++/4.3/bits/vector.tcc:136: instantiated from ‘__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> > std::vector<_Tp, _Alloc>::erase(__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >, __gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >) [with _Tp = const int, _Alloc = std::allocator<const int>]’ Filter.cpp:23: instantiated from ‘Container<A, Allocator> filter(const Container<A, Allocator>&, const Predicate&) [with Container = std::vector, Predicate = bool ()(int), Allocator = std::allocator<const int>, A = const int]’ Filter.cpp:30: instantiated from here /usr/include/c++/4.3/bits/stl_algobase.h:396: error: no matching function for call to ‘std::__copy_move<false, true, std::random_access_iterator_tag>::__copy_m(const int*&, const int*&, const int*&)’ Please tell me what I am doing wrong here and what is the correct way to achieve the kind of higher order polymorphism I want. Thanks.

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• A mysterious compilation error: cannot convert from 'const boost::shared_ptr<T>' to 'const boost::shared_ptr<T>'

  - by Stephane Rolland

  I wanted to protect the access to a log file that I use for multithreaded logging with boostlog library. I tried this stream class class ThreadSafeStream { public: template <typename TInput> const ThreadSafeStream& operator<< (const TInput &tInput) const { // some thread safe file access return *this; } }; using it this way (text_sink is a boostlog object): //... m_spSink.reset(new text_sink); text_sink::locked_backend_ptr pBackend = m_spSink->locked_backend(); const boost::shared_ptr< ThreadSafeStream >& spFileStream = boost::make_shared<ThreadSafeStream>(); pBackend->add_stream(spFileStream); // this causes the compilation error and I get this mysterious error: cannot convert from 'const boost::shared_ptr<T>' to 'const boost::shared_ptr<T>' the whole compile error: Log.cpp(79): error C2664: 'boost::log2_mt_nt5::sinks::basic_text_ostream_backend<CharT>::add_stream' : cannot convert parameter 1 from 'const boost::shared_ptr<T>' to 'const boost::shared_ptr<T> &' 1> with 1> [ 1> CharT=char 1> ] 1> and 1> [ 1> T=ThreadSafeStream 1> ] 1> and 1> [ 1> T=std::basic_ostream<char,std::char_traits<char>> 1> ] 1> Reason: cannot convert from 'const boost::shared_ptr<T>' to 'const boost::shared_ptr<T>' 1> with 1> [ 1> T=ThreadSafeStream 1> ] 1> and 1> [ 1> T=std::basic_ostream<char,std::char_traits<char>> 1> ] 1> No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called I suspect that I am not well defining the operator<<()... but I don't find what is wrong.

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• Allow member to be const while still supporting operator= on the class

  - by LeopardSkinPillBoxHat

  I have several members in my class which are const and can therefore only be initialised via the initialiser list like so: class MyItemT { public: MyItemT(const MyPacketT& aMyPacket, const MyInfoT& aMyInfo) : mMyPacket(aMyPacket), mMyInfo(aMyInfo) { } private: const MyPacketT mMyPacket; const MyInfoT mMyInfo; }; My class can be used in some of our internally defined container classes (e.g. vectors), and these containers require that operator= is defined in the class. Of course, my operator= needs to do something like this: MyItemT& MyItemT::operator=(const MyItemT& other) { mMyPacket = other.mPacket; mMyInfo = other.mMyInfo; return *this; } which of course doesn't work because mMyPacket and mMyInfo are const members. Other than making these members non-const (which I don't want to do), any ideas about how I could fix this?

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• const return value and template instantiation

  - by Rimo

  From Herb Sutter's GotW #6 Return-by-value should normally be const for non-builtin return types. .... Note: Lakos (pg. 618) argues against returning const value, and notes that it is redundant for builtins anyway (for example, returning "const int"), which he notes may interfere with template instantiation. .... While Sutter seems to disagree on whether to return a const value or non-const value when returning an object of a non-built type by value with Lakos, he generally agrees that returning a const value of a built-in type (e.g const int) is not a good idea. While I understand why that is useless because the return value cannot be modified as it is an rvalue, I cannot find an example of how that might interfere with template instantiation. Please give me an example of how having a const qualifier for a return type might interfere with template instantiation.

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• g++ linker can't find const member function

  - by Max

  I have a Point class (with integer members x and y) that has a member function withinBounds that is declared like so: bool withinBounds(const Point&, const Point&) const; and defined like this: bool Point::withinBounds(const Point& TL, const Point& BR) const { if(x < TL.getX()) return false; if(x > BR.getX()) return false; if(y < TL.getY()) return false; if(y > BR.getY()) return false; // Success return true; } and then in another file, I call withinBounds like this: Point pos = currentPlayer->getPosition(); if(pos.withinBounds(topleft, bottomright)) { // code block } This compiles fine, but it fails to link. g++ gives me this error: /home/max/Desktop/Development/YARL/yarl/src/GameData.cpp:61: undefined reference to 'yarl::utility::Point::withinBounds(yarl::utility::Point const&, yarl::utility::Point const&)' When I make the function not const, it links fine. Anyone know the reason why? The linker error looks like it's looking for a non-const version of the function, but I don't know why it would.

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