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• How to detect an overflow in C++ ?

  - by Tim

  Hi, I just wonder if there is some convenient way to detect if overflow happens to any variable of any default data type used in a C++ program during runtime? By convenient, I mean no need to write code to follow each variable if it is in the range of its data type every time its value changes. Or if it is impossible to achieve this, how would you do? For example, float f1=FLT_MAX+1; cout << f1 << endl; doesn't give any error or warning in either compilation with "gcc -W -Wall" or running. Thanks and regards!

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• What's the big difference between those two binary files?

  - by Lela Dax

  These are two files (contained in the tar.bz2) that were generated using a just-in-time compiler for a game engine. The generated code from ui-linux.bin is from a x86_64 gcc compiler and the ui-windows.bin from the same brand of compiler but targetting win x86_64 (mingw-w64). I've attempted to debug a problem that occurs only on the windows version and i stumbled upon what it seems to be different end-binary code. However, the input assembly code was virtually identical (only difference being pointer representations as int). (there's theoretically no winabi/unixabi conflict since that's taken care of by an attribute flag on certain declarations involved). Any idea what it might be that makes these two binary codes different? The C for the mini-compiler and base assembly producing it appears compatible at first glance. http://www0.org/vm/bins.tar.bz2

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• Building elf within Eclipse within Windows

  - by BSchlinker

  Hey guys, I'm having trouble building an Elf file within Eclipse within Windows. It seems that everytime I build, a PE / portable executable for windows is created. I've gone into the Binary Parser section and checked Elf Parser while making sure that everything else is unchecked. However, I continue to end up with a PE which I cannot run on Linux. For clarification, I'm using the Linux GCC toolchain within Eclipse. I've attempted a reinstall of Cygwin -- still experiencing the same issues. Any ideas? Thanks

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• g++ and c++0x specification support

  - by SepiDev

  although it's been said that the support for c++0x new features in g++ are in experimental mode, many gcc developer claimed that you can use most of the new features in your codes and get the program to work. but when I try to compile this simple program it results in segmentation fault. Why? #include <thread> #include <iostream> void my_thread_func() { std::cout<<"hello"<<std::endl; } int main() { std::thread t(my_thread_func); t.join(); } g++ -std=c++0x -Wall -o run main.cc

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• g++ How to get warning on ignoring function return value

  - by ArunSaha

  lint produces some warning like: foo.c XXX Warning 534: Ignoring return value of function bar() From the lint manual 534 Ignoring return value of function 'Symbol' (compare with Location) A function that returns a value is called just for side effects as, for example, in a statement by itself or the left-hand side of a comma operator. Try: (void) function(); to call a function and ignore its return value. See also the fvr, fvo and fdr flags in §5.5 "Flag Options". I want to get this warning, if there exists any, during compilation. Is there any option in gcc/g++ to achieve this? I had turned on -Wall but that apparently did not detect this.

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• Configuring a library to be included with C++ test

  - by vrish88

  Hello, I would like to utilize the UnitTest++ library in a testing file. However, I am having some difficulty getting the library to be included at compile time. So here is my current directory structure: tests/ UnitTests++/ libUnitTest++.a src/ UnitTests++.h unit/ test.cpp I have just used the UnitTest++ getting started guide to just get the library setup. Here is test.cpp: // test.cpp #include <UnitTest++.h> TEST(FailSpectacularly) { CHECK(false); } int main() { return UnitTest::RunAllTests(); } And I am currently trying to compile with: gcc -lUnitTest++ -L../UnitTest++/ -I../UnitTest++/src/ test.cpp I am currently getting a bunch output with ld: symbol(s) not found at the end. So how would I be able to get the UnitTest++ library properly included when this program is compiled? I am on a Mac and I'd also like for there to be an easy way for people on a Linux machine to run these same tests. Whew, I hope this provides enough information, if not please let me know.

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• Removing trailing newline character from fgets() input

  - by sfactor

  i am trying to get some data from the user and send it to another function in gcc. the code is something like this. printf("Enter your Name: "); if(!(fgets(Name, sizeof Name, stdin) != NULL)) { fprintf(stderr, "Error reading Name.\n"); exit(1); } However, i find that it has an \n character in the end. so if i enter John it ends up sending John\n. so how do i remove that \n and send a proper string.

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• Foo f = Foo(); // no matching function for call to 'Foo::Foo(Foo)' ... huh?!

  - by Kyle

  class Foo { public: explicit Foo() {} explicit Foo(Foo&) {} }; Foo d = Foo(); error: no matching function for call to 'Foo::Foo(Foo)' I tried changing Foo(Foo&) to Foo(Foo) as the error suggests, which AFAIK is not a valid constructor, and sure enough I get: error: invalid constructor; you probably meant ‘Foo (const Foo&)’ What gives? How do I resolve this? (This is on GCC by the way)

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• c99 goto past initialization

  - by R Samuel Klatchko

  While debugging a crash, I came across this issue in some code: int func() { char *p1 = malloc(...); if (p1 == NULL) goto err_exit; char *p2 = malloc(...); if (p2 == NULL) goto err_exit; ... err_exit: free(p2); free(p1); return -1; } The problem occurs when the first malloc fails. Because we jump across the initialization of p2, it contains random data and the call to free(p2) can crash. I would expect/hope that this would be treated the same way as in C++ where the compiler does not allow a goto to jump across an initialization. My question: is jumping across an initialization allowed by the standard or is this a bug in gcc's implementation of c99?

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• How can I check that I didn't break anything when refactoring?

  - by Nathan Fellman

  I'm about to embark on a bout of refactoring of some functions in my code. I have a nice amount of unit tests that will ensure I didn't break anything, but I'm not sure about the coverage they give me. Are there any tools that can analyze the code and see that the functionality remains the same? I plan to refactor some rather isolated code, so I don't need to check the entire program, just the areas that I'm working on. For context, the code I'm working on is in C/C++, and I work in Linux with GCC and VIM.

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• How to learn to program C the right way

  - by sfactor

  i have been programming in C/C++ for my academic courses a lot and was under the impression i had a pretty good grasp of it. but lately i had to work in a bluetooth application that had a server and client implementation in a Linux box and an embedded system. i learned bluez bluetooth API, socket/network programming and coded it. however i ran into a lot of problems with memory leaks and segmentation faults and other memory related errors along the way.as the code grew more complex i all but lost control of the pointers and threads and sockets. this got me wondering that i had a lot to learn that they didn't say in the basic C/C++ books. so i wanted to ask for the resources that are available that'll help be code better in a professional way in C/C++ .especially for the Linux/Mac environment (gcc compiler).

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• When compiling programs to run inside a VM, what should march and mtune be set to?

  - by Russ

  With VMs being slave to whatever the host machine is providing, what compiler flags should be provided to gcc? I would normally think that -march=native would be what you would use when compiling for a dedicated box, but the fine detail that -march=native is going to as indicated in this article makes me extremely wary of using it. So... what to set -march and -mtune to inside a VM? For a specific example... My specific case right now is compiling python (and more) in a linux guest inside a KVM-based "cloud" host that I have no real control over the host hardware (aside from 'simple' stuff like CPU GHz m CPU count, and available RAM). Currently, cpuinfo tells me I've got an "AMD Opteron(tm) Processor 6176" but I honestly don't know (yet) if that is reliable and whether the guest can get moved around to different architectures on me to meet the host's infrastructure shuffling needs (sounds hairy/unlikely). All I can really guarantee is my OS, which is a 64-bit linux kernel where uname -m yields x86_64.

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• Why won't C++ allow this default value

  - by nieldw

  Why won't GCC allow a default parameter here? template<class edgeDecor, class vertexDecor, bool dir> Graph<edgeDecor,int,dir> Graph<edgeDecor,vertexDecor,dir>::Dijkstra(vertex s, bool print = false) const { This is the output I get: graph.h:82: error: default argument given for parameter 2 of ‘Graph<edgeDecor, int, dir> Graph<edgeDecor, vertexDecor, dir>::Dijkstra(Vertex<edgeDecor, vertexDecor, dir>, bool)’ graph.h:36: error: after previous specification in ‘Graph<edgeDecor, int, dir> Graph<edgeDecor, vertexDecor, dir>::Dijkstra(Vertex<edgeDecor, vertexDecor, dir>, bool)’ Can anyone see why I'm getting this?

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• Can't inherit from auto_str without problems

  - by fret

  What I want to do is this: #include <memory> class autostr : public std::auto_ptr<char> { public: autostr(char *a) : std::auto_ptr<char>(a) {} autostr(autostr &a) : std::auto_ptr<char>(a) {} // define a bunch of string utils here... }; autostr test(char a) { return autostr(new char(a)); } void main(int args, char **arg) { autostr asd = test('b'); return 0; } (I actually have a copy of the auto_ptr class that handles arrays as well, but the same error applies to the stl one) The compile error using GCC 4.3.0 is: main.cpp:152: error: no matching function for call to `autostr::autostr(autostr)' main.cpp:147: note: candidates are: autostr::autostr(autostr&) main.cpp:146: note: autostr::autostr(char*) I don't understand why it's not matching the autostr argument as a valid parameter to autostr(autostr&).

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• Can't inherit from auto_ptr without problems

  - by fret

  What I want to do is this: #include <memory> class autostr : public std::auto_ptr<char> { public: autostr(char *a) : std::auto_ptr<char>(a) {} autostr(autostr &a) : std::auto_ptr<char>(a) {} // define a bunch of string utils here... }; autostr test(char a) { return autostr(new char(a)); } void main(int args, char **arg) { autostr asd = test('b'); return 0; } (I actually have a copy of the auto_ptr class that handles arrays as well, but the same error applies to the stl one) The compile error using GCC 4.3.0 is: main.cpp:152: error: no matching function for call to `autostr::autostr(autostr)' main.cpp:147: note: candidates are: autostr::autostr(autostr&) main.cpp:146: note: autostr::autostr(char*) I don't understand why it's not matching the autostr argument as a valid parameter to autostr(autostr&).

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• C++'s std::string pools, debug builds? std::string and valgrind problems

  - by Den.Jekk

  Hello, I have a problem with many valgrind warnings about possible memory leaks in std::string, like this one: 120 bytes in 4 blocks are possibly lost in loss record 4,192 of 4,687 at 0x4A06819: operator new(unsigned long) (vg_replace_malloc.c:230) by 0x383B89B8B0: std::string::_Rep::_S_create(unsigned long, unsigned long, std::allocator<char> const&) (in /usr/lib64/libstdc++.so.6.0.8) by 0x383B89C3B4: (within /usr/lib64/libstdc++.so.6.0.8) by 0x383B89C4A9: std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(char const*, unsigned long, std::allocator<char> const&) (in /usr/lib64/libstdc++.so.6.0.8) I'm wondering: does std::string (GCC 4.1.2) use any memory pools? if so, is there any way to disable the pools (in form of a debug build etc.)? Regards, Den

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• Potential problems porting to different architectures

  - by Brendan Long

  I'm writing a Linux program that currently compiles and works fine on x86 and x86_64, and now I'm wondering if there's anything special I'll need to do to make it work on other architectures. What I've heard is that for cross platform code I should: Don't assume anything about the size of a pointer, int or size_t Don't make assumptions about byte order (I don't do any bit shifting -- I assume gcc will optimize my power of two multiplication/division for me) Don't use assembly blocks (obvious) Make sure your libraries work (I'm using SQLite, libcurl and Boost, which all seem pretty cross-platform) Is there anything else I need to worry about? I'm not currently targeting any other architectures, but I expect to support ARM at some point, and I figure I might as well make it work on any architecture if I can. Also, regarding my second point about byte order, do I need to do anything special with text input? I read files with getline(), so it seems like that should be done automatically as well.

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• How to tell the MinGW linker not to export all symbols?

  - by James R.

  Hello, I'm building a Windows dynamic library using the MinGW toolchain. To build this library I'm statically linking to other 2 which offer an API and I have a .def file where I wrote the only symbol I want to be exported in my library. The problem is that GCC is exporting all of the symbols including the ones from the libraries I'm linking to. Is there anyway to tell the linker just to export the symbols in the def file? I know there is the option --export-all-symbols but there seems not to be the opposite to it. Right now the last line of the build script has this structure: g++ -shared CXXFLAGS DEFINES INCLUDES -o library.dll library.cpp DEF_FILE \ OBJECT_FILES LIBS -Wl,--enable-stdcall-fixup EDIT: In the docs about the linker it says that --export-all-symbols is the default behavior and that it's disabled when you don't use that option explicitly if you provide a def file, except when it doesn't; the symbols in 3rd party libs are being exported anyway. EDIT: Adding the option --exclude-libs LIBS doesn't keep their symbols from being exported either.

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• Objective C for Windows

  - by Luther Baker

  What would be the best way to write Objective-C on the Windows platform? Cygwin and gcc? Is there a way I can somehow integrate this into Visual Studio? Along those lines - are there any suggestions as to how to link in and use the Windows SDK for something like this. Its a different beast but I know I can write assembly and link in the Windows DLLs giving me accessibility to those calls but I don't know how to do this without googling and getting piecemeal directions. Is anyone aware of a good online or book resource to do or explain these kinds of things?

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• Compatible types and structures in C

  - by Oli Charlesworth

  I have the following code: int main(void) { struct { int x; } a, b; struct { int x; } c; struct { int x; } *p; b = a; /* OK */ c = a; /* Doesn't work */ p = &a; /* Doesn't work */ return 0; } which fails to compile under GCC (3.4.6), with the following error: test.c:8: error: incompatible types in assignment test.c:9: warning: assignment from incompatible pointer type Now, from what I understand (admittedly from the C99 standard), is that a and c should be compatible types, as they fulfill all the criteria in section 6.2.7, paragraph 1. I've tried compiling with std=c99, to no avail. Presumably my interpretation of the standard is wrong?

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• C optimization breaks algorithm

  - by Halpo

  I am programming an algorithm that contains 4 nested for loops. The problem is at at each level a pointer is updated. The innermost loop only uses 1 of the pointers. The algorithm does a complicated count. When I include a debugging statement that logs the combination of the indexes and the results of the count I get the correct answer. When the debugging statement is omitted, the count is incorrect. The program is compiled with the -O3 option on gcc. Why would this happen?

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• Connect to a website via HTTP in C

  - by sfactor

  i have a C code that parses a file and generates another file for the processed data. i now need to send these files to a web server (website). i guess there way is to do a HTTP POST. but i have never done this in c (Linux gcc compiler in ubuntu). Does anyone know how to do this. i need to a starting point as i have no clue of doing this in C. i also need to be able to authenticate with the website.

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• Building 16 bit os - character array not working

  - by brainbarshan

  Hi. I am building a 16 bit operating system. But character array does not seem to work. Here is my example kernel code: asm(".code16gcc\n"); void putchar(char); int main() { char *str = "hello"; putchar('A'); if(str[0]== 'h') putchar('h'); return 0; } void putchar(char val) { asm("movb %0, %%al\n" "movb $0x0E, %%ah\n" "int $0x10\n" : :"m"(val) ) ; } It prints: A that means putchar function is working properly but if(str[0]== 'h') putchar('h'); is not working. I am compiling it by: gcc -fno-toplevel-reorder -nostdinc -fno-builtin -I./include -c -o ./bin/kernel.o ./source/kernel.c ld -Ttext=0x9000 -o ./bin/kernel.bin ./bin/kernel.o -e 0x0 What should I do?

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• Unmangling the result of std::type_info::name

  - by terminus

  I'm currently working on some logging code that supposed to - among other things - print information about the calling function. This should be relatively easy, standard C++ has a type_info class. This contains the name of the typeid'd class/function/etc. but it's mangled. It's not very usefull. I.e. typeid(std::vector).name() returns "St6vectorIiSaIiEE". Is there a way to produce something usefull from this? Like 'std::vector' for the above example. If it only works for non-template classes, that's fine too. The sollution should work for gcc, but it would be better if I could port it. It's for logging so it's not so important that it can't be turned of, but it should be helpfull for debugging.

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• Ofstream writes empty file on linux

  - by commanderz

  Hi, I have a program which writes its output using ofstream. Everything works perfectly fine on Windows when compiled with Visual Studio, but it only writes empty file on Linux when compiled with GCC. ofstream out(path_out_cstr, ofstream::out); if(out.bad()){ cout << "Could not write the file" << flush; } else{ cout << "writing"; out << "Content" << endl; if(out.fail()) cout << "writing failed"; out.flush(); out.close(); } The directory which is being writen into has 0777 privileges. Thanks for help

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