Clang vs GCC for my Linux Development project

EDIT:

The gcc guys really improved the diagnosis experience in gcc (ah competition). They created a wiki page to showcase it here. gcc 4.8 now has quite good diagnostics as well (gcc 4.9x added color support). Clang is still in the lead, but the gap is closing.

Original:

For students, I would unconditionally recommend Clang.

The performance in terms of generated code between gcc and Clang is now unclear (though I think that gcc 4.7 still has the lead, I haven't seen conclusive benchmarks yet), but for students to learn it does not really matter anyway.

On the other hand, Clang's extremely clear diagnostics are definitely easier for beginners to interpret.

Consider this simple snippet:

#include <string>#include <iostream>struct Student {std::string surname;std::string givenname;}std::ostream& operator<<(std::ostream& out, Student const& s) {  return out << "{" << s.surname << ", " << s.givenname << "}";}int main() {  Student me = { "Doe", "John" };  std::cout << me << "\n";}

You'll notice right away that the semi-colon is missing after the definition of the Student class, right :) ?

Well, gcc notices it too, after a fashion:

prog.cpp:9: error: expected initializer before ‘&’ tokenprog.cpp: In function ‘int main()’:prog.cpp:15: error: no match for ‘operator<<’ in ‘std::cout << me’/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/ostream:112: note: candidates are: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>& (*)(std::basic_ostream<_CharT, _Traits>&)) [with _CharT = char, _Traits = std::char_traits<char>]/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/ostream:121: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ios<_CharT, _Traits>& (*)(std::basic_ios<_CharT, _Traits>&)) [with _CharT = char, _Traits = std::char_traits<char>]/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/ostream:131: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::ios_base& (*)(std::ios_base&)) [with _CharT = char, _Traits = std::char_traits<char>]/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/ostream:169: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long int) [with _CharT = char, _Traits = std::char_traits<char>]/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/ostream:173: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long unsigned int) [with _CharT = char, _Traits = std::char_traits<char>]/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/ostream:177: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(bool) [with _CharT = char, _Traits = std::char_traits<char>]/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/bits/ostream.tcc:97: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short int) [with _CharT = char, _Traits = std::char_traits<char>]/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/ostream:184: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short unsigned int) [with _CharT = char, _Traits = std::char_traits<char>]/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/bits/ostream.tcc:111: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(int) [with _CharT = char, _Traits = std::char_traits<char>]/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/ostream:195: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(unsigned int) [with _CharT = char, _Traits = std::char_traits<char>]/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/ostream:204: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long long int) [with _CharT = char, _Traits = std::char_traits<char>]/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/ostream:208: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long long unsigned int) [with _CharT = char, _Traits = std::char_traits<char>]/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/ostream:213: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(double) [with _CharT = char, _Traits = std::char_traits<char>]/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/ostream:217: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(float) [with _CharT = char, _Traits = std::char_traits<char>]/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/ostream:225: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long double) [with _CharT = char, _Traits = std::char_traits<char>]/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/ostream:229: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(const void*) [with _CharT = char, _Traits = std::char_traits<char>]/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/bits/ostream.tcc:125: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_streambuf<_CharT, _Traits>*) [with _CharT = char, _Traits = std::char_traits<char>]

And Clang is not exactly starring here either, but still:

/tmp/webcompile/_25327_1.cc:9:6: error: redefinition of 'ostream' as different kind of symbolstd::ostream& operator<<(std::ostream& out, Student const& s) {     ^In file included from /tmp/webcompile/_25327_1.cc:1:In file included from /usr/include/c++/4.3/string:49:In file included from /usr/include/c++/4.3/bits/localefwd.h:47:/usr/include/c++/4.3/iosfwd:134:33: note: previous definition is here  typedef basic_ostream<char>           ostream;        ///< @isiosfwd                                        ^/tmp/webcompile/_25327_1.cc:9:13: error: expected ';' after top level declaratorstd::ostream& operator<<(std::ostream& out, Student const& s) {            ^            ;2 errors generated.

I purposefully choose an example which triggers an unclear error message (coming from an ambiguity in the grammar) rather than the typical "Oh my god Clang read my mind" examples. Still, we notice that Clang avoids the flood of errors. No need to scare students away.

As of right now, GCC has much better and more complete support for C++11 features than Clang. Also, the code generator for GCC performs better optimisation than the one in Clang (in my experience, I have not seen any exhaustive tests).

On the other hand, Clang often compiles code more quickly than GCC, and produces better error messages when there is something wrong with your code.

The choice of which one to use really depends on what things are important to you. I value C++11 support and code generation quality more than I value convenience of compilation. Because of this, I use GCC. For you, the trade-offs could be different.

I use both because sometimes they give different, useful error messages.

The Python project was able to find and fix a number of small buglets when one of the core developers first tried compiling with clang.