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  • A short but intense GCC Gathering in London

    - by user817571
    About one week ago I joined in London many long time GCC friends and acquaintances for a gathering organized by Google (in particular I guess should be thanked Diego and Ian). Only a weekend, and I wasn't able to attend on Sunday morning, but a very good occasion to raise some issues in a very relaxed way, in particular those at the border between areas of competence, which are the most difficult to discuss during the normal work days. If you are interested in a general overview and some notes this is a good link: http://gcc.gnu.org/wiki/GCCGathering2011 As you may easily guess, the third topic is mine, which I managed to have up quite early on Friday morning thanks to the votes of some good friends like Dodji (the ordering of the topics resulted from democratic voting on Friday evening!). I learned a lot from the discussion: for example that certainly the new C++11 'final' should be exploited largely in the c++ front-end; the various reasons why devirtualization can be quite trick (but I'm really confident that Martin and Honza are going to make a good progress also basing on a set of short testcases which I promised to collect); that, as explained by Ian, the gold linker already implements the nice --icf (Identical Code Folding) facility, which some friends of mine are definitely going to like (however, see: http://sourceware.org/bugzilla/show_bug.cgi?id=12919). I also enjoyed the observations made by Lawrence, where he remarked that in C+11 we are going to see more pointer iterations implicitly produced by the new range-based for-loop and we really want to make sure the loop optimizers are able to deal with those as well as loops explicitly using a counter. All in all, I really hope we are going to do it again!

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  • Questions about linking libraries in C

    - by james
    I am learning C (still very much a beginner) on Linux using the GCC compiler. I have noticed that some libraries, such as the library used with the math.h header, need to be linked in manually when included. I have been linking in the libraries using various flags of the form -l[library-name], such as -lm for the above-mentioned math library. However, after switching from the command line and/or Geany to Code::Blocks, I noticed that Code::Blocks uses g++ to compile the programs instead of the gcc that I am used to (even though the project is definitely specified as C). Also, Code::Blocks does not require the libraries to be manually linked in when compiling - libraries such as the math library just work. I have two questions: Firstly, is it "bad" to compile C programs with the g++ compiler? So far it seems to work, but after all, C++ is not C and I am quite sure that the g++ compiler is meant for C++. Secondly, is it the g++ compiler that is doing the automatic linking of the libraries in Code::Blocks?

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  • How do .so files avoid problems associated with passing header-only templates like MS dll files have?

    - by Doug T.
    Based on the discussion around this question. I'd like to know how .so files/the ELF format/the gcc toolchain avoid problems passing classes defined purely in header files (like the std library). According to Jan in that answer, the dynamic linker/loader only picks one version of such a class to load if its defined in two .so files. So if two .so files have two definitions, perhaps with different compiler options/etc, the dynamic linker can pick one to use. Is this correct? How does this work with inlining? For example, MSVC inlines templates aggressively. This makes the solution I describe above untenable for dlls. Does Gcc never inline header-only templates like the std library as MSVC does? If so wouldn't that make the functionality of ELF described above ineffective in these cases?

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  • How do I work around the GCC "error: cast from ‘SourceLocation*’ to ‘int’ loses precision" error when compiling cmockery.c?

    - by Daryl Spitzer
    I need to add unit tests using Cmockery to an existing build environment that uses as hand-crafted Makefile. So I need to figure out how to build cmockery.c (without automake). When I run: g++ -DHAVE_CONFIG_H -DPIC -I ../cmockery-0.1.2 -I /usr/include/malloc -c ../cmockery-0.1.2/cmockery.c -o obj/cmockery.o I get a long list of errors like this: ../cmockery-0.1.2/cmockery.c: In function ‘void initialize_source_location(SourceLocation*)’: ../cmockery-0.1.2/cmockery.c:248: error: cast from ‘SourceLocation*’ to ‘int’ loses precision Here are lines 247:248 of cmockery.c: static void initialize_source_location(SourceLocation * const location) { assert_true(location); assert_true is defined on line 154 of cmockery.h: #define assert_true(c) _assert_true((int)(c), #c, __FILE__, __LINE__) So the problem (as the error states) is GCC doesn't like the cast from ‘SourceLocation*’ to ‘int’. I can build Cmockery using ./configure and make (on Linux, and on Mac OS X if I export CFLAGS=-I/usr/include/malloc first), without any errors. I've tried looking at the command-line that compiles cmockery.c when I run make (after ./configure): gcc -DHAVE_CONFIG_H -I. -I. -I./src -I./src -Isrc/google -I/usr/include/malloc -MT libcmockery_la-cmockery.lo -MD -MP -MF .deps/libcmockery_la-cmockery.Tpo -c src/cmockery.c -fno-common -DPIC -o .libs/libcmockery_la-cmockery.o ...but I don't see any options that might work around this error. In "error: cast from 'void*' to 'int' loses precision", I see I could change (int) in cmockery.h to (intptr_t). And I've confirmed that works. But since I can build Cmockery with ./configure and make, there must be a way to get it to build without modifying the source.

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  • "Address of" (&) an array / address of being ignored be gcc?

    - by dbarbosa
    Hi, I am a teaching assistant of a introductory programming course, and some students made this type of error: char name[20]; scanf("%s",&name); which is not surprising as they are learning... What is surprising is that, besides gcc warning, the code works (at least this part). I have been trying to understand and I wrote the following code: void foo(int *str1, int *str2) { if (str1 == str2) printf("Both pointers are the same\n"); else printf("They are not the same\n"); } int main() { int test[50]; foo(&test, test); if (&test == test) printf("Both pointers are the same\n"); else printf("They are not the same\n"); } Compiling and executing: $ gcc test.c -g test.c: In function ‘main’: test.c:12: warning: passing argument 1 of ‘foo’ from incompatible pointer type test.c:13: warning: comparison of distinct pointer types lacks a cast $ ./a.out Both pointers are the same Both pointers are the same Can anyone explain why they are not different? I suspect it is because I cannot get the address of an array (as I cannot have & &x), but in this case the code should not compile.

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  • In C/C++,how to link dynamic link lib which compiled in GCC/G++ in MS VStudio?

    - by coanor
    These days, I use Flex & Bison generated some codes to develop a SQL-parser alike tools, these code can't compiled silently(may be this another topic) in VS2005,but GCC/G++ works well, then I compiled these code with mingw in dll(in windows xp), and then linked these function facades in VS2005, but it seems can't link the dll during linking. Does MS VS2005 recognize the dll which compiled using mingw on windows? Is there anything I need to do additional? For example, adding something in the include-file that declare the exported APIs? Does any one can give some advices? The condition is, as in VS2005, if you want to export some APIs, you may show a *.def file to tell nmake which API you want to export, and then you may create a(or some) *.h file to declare somthing about these APIs(adding some stdcall alike prefix as a call protocal) and some data-type definition. But with GCC/G++, you do not need to do such boring things, just use [ar], you can get these APIs, so my *.h file do not add call protocol and no *.def, just like common function declaration. After *.dll generated, add the *.h file and [mv] generated *.dll in VS2005 project directory, then set the linking *.dll in project setting. Does these steps generated my Question? BTW, I found and tested VC6-compiled dll can be linked with mingw in Windows XP, but the reverse can't work. Anyway, forgive my poor English, and thanks for your concern.

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  • g++ not linking header files properly

    - by cambr
    I am using cygwin libraries to run C and C++ programs on Windows. gcc runs fine, but with g++, I get a long list of errors. I think these erros are because of linking problems with C libraries. Can you suggest what I need to do to fix this? beginning error lines: In file included from testgpp.cpp:1: /cygdrive/c/cygwin/bin/../lib/gcc/i686-pc-cygwin/3.4.4/include/c++/cstdio:52:19: stdio.h: No such file or directory In file included from testgpp.cpp:1: /cygdrive/c/cygwin/bin/../lib/gcc/i686-pc-cygwin/3.4.4/include/c++/cstdio:99: error: `::FILE' has not been declared /cygdrive/c/cygwin/bin/../lib/gcc/i686-pc-cygwin/3.4.4/include/c++/cstdio:100: error: `::fpos_t' has not been declared /cygdrive/c/cygwin/bin/../lib/gcc/i686-pc-cygwin/3.4.4/include/c++/cstdio:102: error: `::clearerr' has not been declared /cygdrive/c/cygwin/bin/../lib/gcc/i686-pc-cygwin/3.4.4/include/c++/cstdio:103: error: `::fclose' has not been declared /cygdrive/c/cygwin/bin/../lib/gcc/i686-pc-cygwin/3.4.4/include/c++/cstdio:104: error: `::feof' has not been declared the whole error dump: PasteBin

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  • Python module: Trouble Installing Bitarray 0.8.0 on Mac OSX 10.7.4

    - by Gabriele
    I'm new here! I have trouble installing bitarray (vers 0.8.0) on my Mac OSX 10.7.4. Thanks! ('gcc' does not seem to be the problem) Last login: Sun Sep 9 22:24:25 on ttys000 host-001:~ gabriele$ gcc -version i686-apple-darwin11-llvm-gcc-4.2: no input files host-001:~ gabriele$ Last login: Sun Sep 9 22:18:41 on ttys000 host-001:~ gabriele$ cd /Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/bitarray-0.8.0/ host-001:bitarray-0.8.0 gabriele$ python2.7 setup.py installrunning install running bdist_egg running egg_info creating bitarray.egg-info writing bitarray.egg-info/PKG-INFO writing top-level names to bitarray.egg-info/top_level.txt writing dependency_links to bitarray.egg-info/dependency_links.txt writing manifest file 'bitarray.egg-info/SOURCES.txt' reading manifest file 'bitarray.egg-info/SOURCES.txt' writing manifest file 'bitarray.egg-info/SOURCES.txt' installing library code to build/bdist.macosx-10.6-intel/egg running install_lib running build_py creating build creating build/lib.macosx-10.6-intel-2.7 creating build/lib.macosx-10.6-intel-2.7/bitarray copying bitarray/__init__.py -> build/lib.macosx-10.6-intel-2.7/bitarray copying bitarray/test_bitarray.py -> build/lib.macosx-10.6-intel-2.7/bitarray running build_ext building 'bitarray._bitarray' extension creating build/temp.macosx-10.6-intel-2.7 creating build/temp.macosx-10.6-intel-2.7/bitarray gcc-4.2 -fno-strict-aliasing -fno-common -dynamic -isysroot /Developer/SDKs/MacOSX10.6.sdk -arch i386 -arch x86_64 -g -O2 -DNDEBUG -g -O3 -I/Library/Frameworks/Python.framework/Versions/2.7/include/python2.7 -c bitarray/_bitarray.c -o build/temp.macosx-10.6-intel-2.7/bitarray/_bitarray.o unable to execute gcc-4.2: No such file or directory error: command 'gcc-4.2' failed with exit status 1 host-001:bitarray-0.8.0 gabriele$

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  • C/GCC - Is it possible to sort arrays using preprocessor?

    - by psihodelia
    I have a number of very long arrays. No run-time sort is possible. It is also time consuming to sort them manually. Moreover, new elements can be added in any order later, so I would like to sort them by value using C preprocessor or maybe there is any compilers flag (GCC)? For example: sometype S[] = { {somevals, "BOB", someothervals}, {somevals, "ALICE", someothervals}, {somevals, "TIM", someothervals}, } must be sorted so: sometype S[] = { {somevals, "ALICE", someothervals}, {somevals, "BOB", someothervals}, {somevals, "TIM", someothervals}, }

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  • How can I compile GCC as a static binary?

    - by CaCl
    How can I compile the GCC Compiler so that I can pull the entire thing over to another system and use the program? I don't mind pulling in other files as well, but is there a way to gather all the required system libs as well? The OS and Arch will remain constant across the different systems, but one may contain Slackware where the other contains Debian.

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  • gcc : Is using -Werror and -pedantic considered good practice?

    - by Helper Method
    I'm just digging into the gcc manual and some things are still unclear to me: When specifying a std, should I always use -pedantic in conjunction? When using -g, it the standard level sufficient or should I specify level 3, i.e. -g3? Is it good practice to use -Werror to promote all warnings to errors and -pedantic-errors to promote all pedantic warnings to errors?

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  • Can you explain why gcc -S output something like assemble?

    - by Mask
    $ gcc -S buffer-overflow.c && cat buffer-overflow.s _foo: pushl %ebp ;2 movl %esp, %ebp ;3 subl $16, %esp ;4 movl LC1, %eax ;5 movl %eax, -4(%ebp) ;6 leal -4(%ebp), %eax ;7 leal 8(%eax), %edx ;8 movl $_bad, %eax ;9 movl %eax, (%edx) ;10 leave ret _main: ... call _foo ;1 ... The help information says it should not compile nor assemble: -S Compile only; do not assemble or link Why are they contradictory?

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  • gcc - using -werror and -std= -pedantic considered good practice?

    - by Helper Method
    I'm just digging into the gcc manual and some things are still unclear to me: a) When specifying a std, should I always use -pedantic in conjunction? b) When using -g, it the standard level sufficient or should I specify level 3, i.e. -g3? c) Is it good practice to use -Werror to promote all warnings to errors and -pedantic-errors to promote all pedantic warnings to errors?

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  • Mixing libraries with and without RTTI with GCC on Mac OS X?

    - by Steve the Plant
    I've been banging my head on an issue and before I continue injuring myself some more, I'd like to confirm: Is it possible to have a GCC project that uses libraries that are compiled with and without RTTI? So, for example, I have project A (compiled without RTTI) that uses library B (compiled with RTTI) and library C (compiled without RTTI). In theory, is all that supposed to compile and link with no problems?

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  • gcc optimization? bug? and its practial implication to project

    - by kumar_m_kiran
    Hi All, My questions are divided into three parts Question 1 Consider the below code, #include <iostream> using namespace std; int main( int argc, char *argv[]) { const int v = 50; int i = 0X7FFFFFFF; cout<<(i + v)<<endl; if ( i + v < i ) { cout<<"Number is negative"<<endl; } else { cout<<"Number is positive"<<endl; } return 0; } No specific compiler optimisation options are used or the O's flag is used. It is basic compilation command g++ -o test main.cpp is used to form the executable. The seemingly very simple code, has odd behaviour in SUSE 64 bit OS, gcc version 4.1.2. The expected output is "Number is negative", instead only in SUSE 64 bit OS, the output would be "Number is positive". After some amount of analysis and doing a 'disass' of the code, I find that the compiler optimises in the below format - Since i is same on both sides of comparison, it cannot be changed in the same expression, remove 'i' from the equation. Now, the comparison leads to if ( v < 0 ), where v is a constant positive, So during compilation itself, the else part cout function address is added to the register. No cmp/jmp instructions can be found. I see that the behaviour is only in gcc 4.1.2 SUSE 10. When tried in AIX 5.1/5.3 and HP IA64, the result is as expected. Is the above optimisation valid? Or, is using the overflow mechanism for int not a valid use case? Question 2 Now when I change the conditional statement from if (i + v < i) to if ( (i + v) < i ) even then, the behaviour is same, this atleast I would personally disagree, since additional braces are provided, I expect the compiler to create a temporary built-in type variable and them compare, thus nullify the optimisation. Question 3 Suppose I have a huge code base, an I migrate my compiler version, such bug/optimisation can cause havoc in my system behaviour. Ofcourse from business perspective, it is very ineffective to test all lines of code again just because of compiler upgradation. I think for all practical purpose, these kinds of error are very difficult to catch (during upgradation) and invariably will be leaked to production site. Can anyone suggest any possible way to ensure to ensure that these kind of bug/optimization does not have any impact on my existing system/code base? PS : When the const for v is removed from the code, then optimization is not done by the compiler. I believe, it is perfectly fine to use overflow mechanism to find if the variable is from MAX - 50 value (in my case).

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  • C++: Why does gcc prefer non-const over const when accessing operator[]?

    - by JonasW
    This question might be more appropriately asked regarding C++ in general, but as I am using gcc on linux that's the context. Consider the following program: #include <iostream> #include <map> #include <string> using namespace std; template <typename TKey, typename TValue> class Dictionary{ public: map<TKey, TValue> internal; TValue & operator[](TKey const & key) { cout << "operator[] with key " << key << " called " << endl; return internal[key]; } TValue const & operator[](TKey const & key) const { cout << "operator[] const with key " << key << " called " << endl; return internal.at(key); } }; int main(int argc, char* argv[]) { Dictionary<string, string> dict; dict["1"] = "one"; cout << "first one: " << dict["1"] << endl; return 0; } When executing the program, the output is: operator[] with key 1 called operator[] with key 1 called first one: one What I would like is to have the compiler choose the operator[]const method instead in the second call. The reason is that without having used dict["1"] before, the call to operator[] causes the internal map to create the data that does not exist, even if the only thing I wanted was to do some debugging output, which of course is a fatal application error. The behaviour I am looking for would be something like the C# index operator which has a get and a set operation and where you could throw an exception if the getter tries to access something that doesn't exist: class MyDictionary<TKey, TVal> { private Dictionary<TKey, TVal> dict = new Dictionary<TKey, TVal>(); public TVal this[TKey idx] { get { if(!dict.ContainsKey(idx)) throw KeyNotFoundException("..."); return dict[idx]; } set { dict[idx] = value; } } } Thus, I wonder why the gcc prefers the non-const call over the const call when non-const access is not required.

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