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• Rounding issue when adding floats in python, is this normal?

  - by thepearson

  I just wanted to know if this behavior is expected. If so, can someone explain to me why. This has probably been answered elsewhere I can't seem to find it using Google. Probably not searching with the right terms. I am running Ubuntu 10.04. Python 2.6.5 (r265:79063, Apr 16 2010, 13:09:56) [GCC 4.4.3] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> var = 10.0 >>> var 10.0 >>> var + 5 15.0 >>> var + 5.1 15.1 >>> var + 5.2 15.199999999999999 >>>

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• Is "}while(0);" always equal to "break;}while(1);" ?

  - by Hernán Eche

  I have compared gcc assembler output of do{ //some code }while(0); with do{ //some code break; }while(1); The output is equal, with or without optimization but.. It's always that way? No experiment can prove theories, they can only show they are wrong And because (I hope) programming is not an experimental science, and results can be predicted (at least simple things) I want to be sure next time I reeplace a break;}while(1); for the clearer (and less risky) while(0); Thank you for reading

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• C++ performance, optimizing compiler, empty function in .cpp

  - by Dodo

  I've a very basic class, name it Basic, used in nearly all other files in a bigger project. In some cases, there needs to be debug output, but in release mode, this should not be enabled and be a NOOP. Currently there is a define in the header, which switches a makro on or off, depending on the setting. So this is definetely a NOOP, when switched off. I'm wondering, if I have the following code, if a compiler (MSVS / gcc) is able to optimize out the function call, so that it is again a NOOP. (By doing that, the switch could be in the .cpp and switching will be much faster, compile/link time wise). --Header-- void printDebug(const Basic* p); class Basic { Basic() { simpleSetupCode; // this should be a NOOP in release, // but constructor could be inlined printDebug(this); } }; --Source-- // PRINT_DEBUG defined somewhere else or here #if PRINT_DEBUG void printDebug(const Basic* p) { // Lengthy debug print } #else void printDebug(const Basic* p) {} #endif

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• Delay-Load equivalent in unix based systems

  - by saran

  What is the delay load equivalent in unix based system. I have a code foo.cpp, While compiling with gcc I link it to shared objects(totally three .so files are there.).Each of the .so file for different option. ./foo -v needs libversion.so ./foo -update needs libupdate.so I need the symbol for those libraries should be resolved only at the run time. ./foo -v should not break even if libupdate.so library is not there. It is working in windows using the delay load option(in properties of dll). What is its equivalent in unix systems. Will '-lazy' option does the same in UNIX?. If so,Where to include this option? (in makefile or with linker ld). I am not good in unix. Please help me.. Thanks in advance.

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• Forward declaring an enum in c++

  - by szevvy

  Hi guys, I'm trying to do something like the following: enum E; void Foo(E e); enum E {A, B, C}; which the compiler rejects. I've had a quick look on Google and the consensus seems to be "you can't do it", but I can't understand why. Can anyone explain? Many thanks. Clarification 2: I'm doing this as I have private methods in a class that take said enum, and I do not want the enum's values exposed - so, for example, I do not want anyone to know that E is defined as enum E { FUNCTIONALITY_NORMAL, FUNCTIONALITY_RESTRICTED, FUNCTIONALITY_FOR_PROJECT_X } as project X is not something I want my users to know about. So, I wanted to forward declare the enum so I could put the private methods in the header file, declare the enum internally in the cpp, and distribute the built library file and header to people. As for the compiler - it's GCC.

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• const ready only local copies

  - by robUK

  Hello gcc 4.4.4 c89 I am just wondering is it worth passing a const into a function. i.e. void do_something(const char *dest, const int size) The size is a ready-only so I don't want to change it. However, some developers never have this as const has it is a local copy that is being used. The pointer is const as you can change the value in the calling routine. I always have a const on ready-only local copies, as it confirms to anyone reading my code that it is a ready-only variable. And also, when coding I don't make the mistake of changing it without realizing. Many thanks for any suggestions,

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• Debuggin in Xcode

  - by huggie

  I'm toying with iPhone app development. Often times I would run into runtime error and I would have no idea where the error occurs (e.g. the exact line). In console app with GCC I could at least compile with the -g flag. dump a core file and read that core file in to get to the last line that got into trouble. But how would I do that in Xcode? Build and Debug doesn't seem to have the debugging symbol loaded.

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• how to compile youtube-api appliation

  - by Gpathy

  Hi, i am developing a custom Youtube video player. But i am not able to compile the program. I am missing something in Makefile. My program looks like main.c #include<gdata/services/youtube/gdata-youtube-service.h> int main(int argc, char **argv[]) { printf("Youtube Application\n"); return 0; } makefile gcc `pkg-config --cflags --libs libgdata-google-1.2`  -lgdata-google-1.2 main.c -o youtube When i compile, it is giving error like error: gdata/services/youtube/gdata-youtube-service.h: No such file or directory Do i got to install some other packages ? Or, i need to include something in my Makefile ? Thanks...

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• Problems with variadic macros in C

  - by imikedaman

  Hi, I'm having a problem with optional arguments in #define statements in C, or more specifically with gcc 4.2: bool func1(bool tmp) { return false; } void func2(bool tmp, bool tmp2) {} #define CALL(func, tmp, ...) func(tmp, ##__VA_ARGS__) int main() { // this compiles CALL(func2, CALL(func1, false), false); // this fails with: Implicit declaration of function 'CALL' CALL(func2, false, CALL(func1, false)); } That's obviously a contrived example, but does show the problem. Does anyone know how I can get the optional arguments to "resolve" correctly? Additional information: If I remove the ## before _VA_ARGS_, and do something like this: bool func2(bool tmp, bool tmp2) { return false; } #define CALL(func, tmp, ...) func(tmp, __VA_ARGS__) int main() { CALL(func2, false, CALL(func2, false, false)); } That compiles, but it no longer works with zero arguments since it would resolve to func(tmp, )

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• C++0x optimizing compiler quality

  - by aaa

  hello. I do some heavy numbercrunching and for me floating-point performance is very important. I like performance of Intel compiler very much and quite content with quality of assembly it produces. I am thinking at some point to try C++0x mainly for sugar parts, like auto, initializer list, etc, but also lambdas. at this point I use those features in regular C++ by the means of boost. How good of assembly code do compilers C++0x generate? specifically Intel and gcc compilers. Do they produce SSE code? is performance comparable to C++? are there any benchmarks? My Google search did not reveal much. Thank you.

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• Compiling C-dll for Python OR SWIG-module creation, how to continue ??

  - by ljuju

  I reference this file "kbdext.c" and its headerfile listed on http://www.docdroppers.org/wiki/index.php?title=Writing_Keyloggers (the listings are at the bottom). I've been trying to compile this into a dll for use in Python or Visual Basic, but have not succeeded. I'm not familiar with C or GCC to sort out the problems or do the dll compile correctly. (I also get an error about snprintf not being declared when doing a regular compile of all the files). What are the steps I should do to make all functions available for other languages and external apps? Or is it perhaps easier to use SWIG and make a python module, instead of compiling a DLL?

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• C++ and preprocessor macro gotcha

  - by aaa

  hello. Appologies for yet another gotcha question. Can you figure out what is wrong with the statement below? gcc error states: "type name declared as function returning array". #define MACRO(a) (a)[1] class index { typedef int index_type[2]; index_type& operator[](int i); }; int k = 0; int i = MACRO(index()[k]); ps: is such questions are deemed too annoying, I am going to stop.

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• What causes Python "Interpreter not Initialized" error?

  - by ?????

  I'm now on my third full day this week of trying to get OpenCV to work with Python. (I have been trying on and off for the past 6 months). I get this error Python 2.7.1 (r271:86882M, Nov 30 2010, 10:35:34) [GCC 4.2.1 (Apple Inc. build 5664)] on darwin Type "help", "copyright", "credits" or "license" for more information. dlopen("/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-dynload/readline.so", 2); import readline # dynamically loaded from /Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-dynload/readline.so >>> import cv dlopen("./cv.so", 2); Fatal Python error: Interpreter not initialized (version mismatch?) and then it crashes (core dumps). python -v gives nothing after the dlopen. Any ideas from anyone who actually knows about this error?

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• The D Programming Language for Game Development

  - by n2liquid

  Hi all, Recently I've been bothered because I reached a point in which C++ (even 0x) felt very limited, so I started looking for alternatives. Forget Java, C#, Python or Ruby. I still like the low-level nature of C++ and I'm not fond of virtual machines. Further, I'm a game engine developer, so I have to develop core routines which must be really fast, and lately I've been hungry for code expressiveness. C++ is an almost-there language for me, but there are many exceptions on how to use templates, and GCC isn't optimizing stuff as well as I'd hoped it would. So I'm considering to start learning D. Do you think it will suffice my needs as a game developer? I'm weary because I've never heard of D being used for that. Thanks!

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• Use C function in C++ program; "multiply-defined" error

  - by eom

  I am trying to use this code for the Porter stemming algorithm in a C++ program I've already written. I followed the instructions near the end of the file for using the code as a separate module. I created a file, stem.c, that ends after the definition and has extern int stem(char * p, int i, int j) ... It worked fine in Xcode but it does not work for me on Unix with gcc 4.1.1--strange because usually I have no problem moving between the two. I get the error ld: fatal: symbol `stem(char*, int, int)' is multiply-defined: (file /var/tmp//ccrWWlnb.o type=FUNC; file /var/tmp//cc6rUXka.o type=FUNC); ld: fatal: File processing errors. No output written to cluster I've looked online and it seems like there are many things I could have wrong, but I'm not sure what combination of a header file, extern "C", etc. would work.

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• Why "constructor-way" of declaring variable in "for-loop" allowed but in "if-statement" not allowed?

  - by PiotrNycz

  Consider this simple example: /*1*/ int main() { /*2*/ for (int i(7); i;){break;} /*3*/ if (int i(7)) {} /*4*/ } Why line-2 compiles just fine, whilst line-3 gives the error? This is little strange to me why if-statement is in this aspect treated worse than for-loop? If this is compiler specific - I tested with gcc-4.5.1: prog.cpp: In function 'int main()': prog.cpp:3:7: error: expected primary-expression before 'int' prog.cpp:3:7: error: expected ')' before 'int' I was inspired by this question [UPDATE] I know this compiles just fine: /*1*/ int main() { /*2*/ for (int i = 7; i;){break;} /*3*/ if (int i = 7) {} /*4*/ }

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• Using concurrently 2 versions of boost

  - by idimba

  I'm using RHEL 5.3, which is shipped with gcc 4.1.2 and boost 1.33. There're some features I want, that are missing in the boost 1.33. Therefore the thought was to upgrade to fresh boost release 1.43. Is it possible to use concurrently some header-only library(s) from boost 1.43 and the rest from 1.33? For example I want to use unorded_map, which is missing in boost 1.33. Is it possible to use concurrently binary boost libraries from different releases?

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• Fast comparison of char arrays?

  - by StackedCrooked

  I'm currently working in a codebase where IPv4 addresses are represented as pointers to u_int8. The equality operator is implemented like this: bool Ipv4Address::operator==(const u_int8 * inAddress) const { return (*(u_int32*) this->myBytes == *(u_int32*) inAddress); } This is probably the fasted solution, but it causes the GCC compiler warning: ipv4address.cpp:65: warning: dereferencing type-punned pointer will break strict-aliasing rules How can I rewrite the comparison correctly without breaking strict-aliasing rules and without losing performance points? I have considered using either memcmp or this macro: #define IS_EQUAL(a, b) \ (a[0] == b[0] && a[1] == b[1] && a[2] == b[2] && a[3] == b[3]) I'm thinking that the macro is the fastest solution. What do you recommend?

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• Problem with optional arguments in C #defines

  - by imikedaman

  Hi, I'm having a problem with optional arguments in #define statements in C, or more specifically with gcc 4.2: bool func1(bool tmp) { return false; } void func2(bool tmp, bool tmp2) {} #define CALL(func, tmp, ...) func(tmp, ##__VA_ARGS__) int main() { // this compiles CALL(func2, CALL(func1, false), false); // this fails with: Implicit declaration of function 'CALL' CALL(func2, false, CALL(func1, false)); } That's obviously a contrived example, but does show the problem. Does anyone know how I can get the optional arguments to "resolve" correctly? Additional information: If I remove the ## before _VA_ARGS_, and do something like this: bool func2(bool tmp, bool tmp2) { return false; } #define CALL(func, tmp, ...) func(tmp, __VA_ARGS__) int main() { CALL(func2, false, CALL(func2, false, false)); } That compiles, but it no longer works with zero arguments since it would resolve to func(tmp, )

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• Complete state of a process

  - by sravan

  hi all, I wrote a small program which is as follows: #include<stdio.h> int c=0; int main() { int a=10,b=20; printf("Hello World\n"); c = a+b; printf("%d\n",c); return 0; } I can create a.out file using the command gcc -save-temps helloworld.c. The save-temps flag allows us to save the intermediate files, helloworld.i, helloworld.s, helloworld.o Now i want to know exactly how the stack of this program changes during the execution. Can some one please tell me how to go about it. My aim of this question is to know exactly what all happens during the execution of any program.

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• C pointer initialization and dereferencing, what's wrong here?

  - by randombits

  This should be super simple, but I'm not sure why the compiler is complaining here. #include <stdio.h> #include <stdlib.h> int main(int argc, char *argv[]) { int *n = 5; printf ("n: %d", *n); exit(0); } Getting the following complaints: foo.c: In function ‘main’: foo.c:6: warning: initialization makes pointer from integer without a cast I just want to print the value that the pointer n references. I'm dereferencing it in the printf() statement and I get a segmentation fault. Compiling this with gcc -o foo foo.c.

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• How could my code compliled correctly without necessary headers?

  - by ZhengZhiren

  I use the functions fork(),exec()... But how can this program compiled without including some extra headers(like sys/types.h, sys/wait.h). I use ubuntu 10.04 with gcc version 4.4.3 #include <stdio.h> #include <stdlib.h> int main() { pid_t pid; printf("before fork\n"); pid = fork(); if(pid == 0) { /*child*/ if(execvp("./cpuid", NULL)) { printf("error\n"); exit(0); } } else { if(wait(NULL) != -1) { printf("ok\n"); } } return 0; }

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• Why is this C or C++ macro not expanded by the preprocessor?

  - by Atul

  Can someone points me the problem in the code when compiled with gcc 4.1.0. #define X 10 int main() { double a = 1e-X; return 0; } I am getting error:Exponent has no digits. When i replace X with 10, it works fine. Also i checked with g++ -E command to see the file with preprocessors applied, it has not replaced X with 10. I was under the impression that preprocessor replaces every macro defined in the file with the replacement text with applying any intelligence. Am I wrong? I know this is a really silly question but I am confused and I would rather be silly than confused :). Any comments/suggestions.

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• Testing for the presence of a character in an string in C

  - by Prab

  What's wrong with this? #include <stdio.h> void main(){ char *s="some text"; printf("%d",is_in(s,'t')); } int is_in(char *s, char c){ while(*s){ if(*s==c) return 1; s++; } return 0; } I get the following compile time error with GCC: test.c:9: error: conflicting types for ‘is_in’ test.c:9: note: an argument type that has a default promotion can’t match an empty parameter name list declaration test.c:5: note: previous implicit declaration of ‘is_in’ was here

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• Is allocating a dynamic array without specifying size well formed code?

  - by Als

  The following simple program snippet gives compilation errorswith gcc-4.3.4. Program: int main() { char *ptr = new char[10]; char *ptr1 = new char[]; return 0; } Compilation errors: prog.cpp: In function ‘int main()’: prog.cpp:4: error: expected primary-expression before ‘]’ token prog.cpp:3: warning: unused variable ‘ptr’ prog.cpp:4: warning: unused variable ‘ptr1’ But the same compiles cleanly with MSVC without any diagnostic message. So my question is: Does the Standard allow an new [] to be called without specifying the size? Or this a bug in MSVC? Can someone provide a reference from the standard which will conclusively say that the above code example is ill-formed or well-formed? I have had a look at: 5.3.4 New [expr.new] & 18.4.1.2 Array forms [lib.new.delete.array] but couldnt find any conclusive evidence about the behavior.

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