Template error messages are fun to decipher. Consider this:
#include <vector>#include <algorithm>int main(){ int a; std::vector< std::vector <int> > v; std::vector< std::vector <int> >::const_iterator it = std::find( v.begin(), v.end(), a );}Compiling with gcc -c error.cpp (4.6.3) will produce 15786 bytes of output, with a longest line of 330 characters.
In file included from /usr/include/c++/4.6/algorithm:63:0, from error_code.cpp:2:/usr/include/c++/4.6/bits/stl_algo.h: In function ‘_RandomAccessIterator std::__find(_RandomAccessIterator, _RandomAccessIterator, const _Tp&, std::random_access_iterator_tag) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator*, std::vector >>, _Tp = int]’:/usr/include/c++/4.6/bits/stl_algo.h:4403:45: instantiated from ‘_IIter std::find(_IIter, _IIter, const _Tp&) [with _IIter = __gnu_cxx::__normal_iterator*, std::vector >>, _Tp = int]’error_code.cpp:8:89: instantiated from here/usr/include/c++/4.6/bits/stl_algo.h:162:4: error: no match for ‘operator==’ in ‘__first.__gnu_cxx::__normal_iterator::operator* [with _Iterator = std::vector*, _Container = std::vector >, __gnu_cxx::__normal_iterator::reference = std::vector&]() == __val’/usr/include/c++/4.6/bits/stl_algo.h:162:4: note: candidates are:/usr/include/c++/4.6/bits/stl_pair.h:201:5: note: template bool std::operator==(const std::pair&, const std::pair&)/usr/include/c++/4.6/bits/stl_iterator.h:285:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)/usr/include/c++/4.6/bits/stl_iterator.h:335:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)/usr/include/c++/4.6/bits/allocator.h:122:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)/usr/include/c++/4.6/bits/allocator.h:127:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)/usr/include/c++/4.6/bits/stl_vector.h:1273:5: note: template bool std::operator==(const std::vector&, const std::vector&)/usr/include/c++/4.6/ext/new_allocator.h:123:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::new_allocator&, const __gnu_cxx::new_allocator&)/usr/include/c++/4.6/bits/stl_iterator.h:805:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)/usr/include/c++/4.6/bits/stl_iterator.h:799:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)/usr/include/c++/4.6/bits/stl_algo.h:4403:45: instantiated from ‘_IIter std::find(_IIter, _IIter, const _Tp&) [with _IIter = __gnu_cxx::__normal_iterator*, std::vector >>, _Tp = int]’error_code.cpp:8:89: instantiated from here/usr/include/c++/4.6/bits/stl_algo.h:166:4: error: no match for ‘operator==’ in ‘__first.__gnu_cxx::__normal_iterator::operator* [with _Iterator = std::vector*, _Container = std::vector >, __gnu_cxx::__normal_iterator::reference = std::vector&]() == __val’/usr/include/c++/4.6/bits/stl_algo.h:166:4: note: candidates are:/usr/include/c++/4.6/bits/stl_pair.h:201:5: note: template bool std::operator==(const std::pair&, const std::pair&)/usr/include/c++/4.6/bits/stl_iterator.h:285:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)/usr/include/c++/4.6/bits/stl_iterator.h:335:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)/usr/include/c++/4.6/bits/allocator.h:122:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)/usr/include/c++/4.6/bits/allocator.h:127:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)/usr/include/c++/4.6/bits/stl_vector.h:1273:5: note: template bool std::operator==(const std::vector&, const std::vector&)/usr/include/c++/4.6/ext/new_allocator.h:123:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::new_allocator&, const __gnu_cxx::new_allocator&)/usr/include/c++/4.6/bits/stl_iterator.h:805:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)/usr/include/c++/4.6/bits/stl_iterator.h:799:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)/usr/include/c++/4.6/bits/stl_algo.h:170:4: error: no match for ‘operator==’ in ‘__first.__gnu_cxx::__normal_iterator::operator* [with _Iterator = std::vector*, _Container = std::vector >, __gnu_cxx::__normal_iterator::reference = std::vector&]() == __val’/usr/include/c++/4.6/bits/stl_algo.h:170:4: note: candidates are:/usr/include/c++/4.6/bits/stl_pair.h:201:5: note: template bool std::operator==(const std::pair&, const std::pair&)/usr/include/c++/4.6/bits/stl_iterator.h:285:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)/usr/include/c++/4.6/bits/stl_iterator.h:335:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)/usr/include/c++/4.6/bits/allocator.h:122:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)/usr/include/c++/4.6/bits/allocator.h:127:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)/usr/include/c++/4.6/bits/stl_vector.h:1273:5: note: template bool std::operator==(const std::vector&, const std::vector&)/usr/include/c++/4.6/ext/new_allocator.h:123:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::new_allocator&, const __gnu_cxx::new_allocator&)/usr/include/c++/4.6/bits/stl_iterator.h:805:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)/usr/include/c++/4.6/bits/stl_iterator.h:799:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)/usr/include/c++/4.6/bits/stl_algo.h:174:4: error: no match for ‘operator==’ in ‘__first.__gnu_cxx::__normal_iterator::operator* [with _Iterator = std::vector*, _Container = std::vector >, __gnu_cxx::__normal_iterator::reference = std::vector&]() == __val’/usr/include/c++/4.6/bits/stl_algo.h:174:4: note: candidates are:/usr/include/c++/4.6/bits/stl_pair.h:201:5: note: template bool std::operator==(const std::pair&, const std::pair&)/usr/include/c++/4.6/bits/stl_iterator.h:285:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)/usr/include/c++/4.6/bits/stl_iterator.h:335:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)/usr/include/c++/4.6/bits/allocator.h:122:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)/usr/include/c++/4.6/bits/allocator.h:127:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)/usr/include/c++/4.6/bits/stl_vector.h:1273:5: note: template bool std::operator==(const std::vector&, const std::vector&)/usr/include/c++/4.6/ext/new_allocator.h:123:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::new_allocator&, const __gnu_cxx::new_allocator&)/usr/include/c++/4.6/bits/stl_iterator.h:805:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)/usr/include/c++/4.6/bits/stl_iterator.h:799:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)/usr/include/c++/4.6/bits/stl_algo.h:182:4: error: no match for ‘operator==’ in ‘__first.__gnu_cxx::__normal_iterator::operator* [with _Iterator = std::vector*, _Container = std::vector >, __gnu_cxx::__normal_iterator::reference = std::vector&]() == __val’/usr/include/c++/4.6/bits/stl_algo.h:182:4: note: candidates are:/usr/include/c++/4.6/bits/stl_pair.h:201:5: note: template bool std::operator==(const std::pair&, const std::pair&)/usr/include/c++/4.6/bits/stl_iterator.h:285:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)/usr/include/c++/4.6/bits/stl_iterator.h:335:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)/usr/include/c++/4.6/bits/allocator.h:122:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)/usr/include/c++/4.6/bits/allocator.h:127:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)/usr/include/c++/4.6/bits/stl_vector.h:1273:5: note: template bool std::operator==(const std::vector&, const std::vector&)/usr/include/c++/4.6/ext/new_allocator.h:123:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::new_allocator&, const __gnu_cxx::new_allocator&)/usr/include/c++/4.6/bits/stl_iterator.h:805:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)/usr/include/c++/4.6/bits/stl_iterator.h:799:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)/usr/include/c++/4.6/bits/stl_algo.h:186:4: error: no match for ‘operator==’ in ‘__first.__gnu_cxx::__normal_iterator::operator* [with _Iterator = std::vector*, _Container = std::vector >, __gnu_cxx::__normal_iterator::reference = std::vector&]() == __val’/usr/include/c++/4.6/bits/stl_algo.h:186:4: note: candidates are:/usr/include/c++/4.6/bits/stl_pair.h:201:5: note: template bool std::operator==(const std::pair&, const std::pair&)/usr/include/c++/4.6/bits/stl_iterator.h:285:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)/usr/include/c++/4.6/bits/stl_iterator.h:335:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)/usr/include/c++/4.6/bits/allocator.h:122:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)/usr/include/c++/4.6/bits/allocator.h:127:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)/usr/include/c++/4.6/bits/stl_vector.h:1273:5: note: template bool std::operator==(const std::vector&, const std::vector&)/usr/include/c++/4.6/ext/new_allocator.h:123:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::new_allocator&, const __gnu_cxx::new_allocator&)/usr/include/c++/4.6/bits/stl_iterator.h:805:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)/usr/include/c++/4.6/bits/stl_iterator.h:799:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)/usr/include/c++/4.6/bits/stl_algo.h:190:4: error: no match for ‘operator==’ in ‘__first.__gnu_cxx::__normal_iterator::operator* [with _Iterator = std::vector*, _Container = std::vector >, __gnu_cxx::__normal_iterator::reference = std::vector&]() == __val’/usr/include/c++/4.6/bits/stl_algo.h:190:4: note: candidates are:/usr/include/c++/4.6/bits/stl_pair.h:201:5: note: template bool std::operator==(const std::pair&, const std::pair&)/usr/include/c++/4.6/bits/stl_iterator.h:285:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)/usr/include/c++/4.6/bits/stl_iterator.h:335:5: note: template bool std::operator==(const std::reverse_iterator&, const std::reverse_iterator&)/usr/include/c++/4.6/bits/allocator.h:122:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)/usr/include/c++/4.6/bits/allocator.h:127:5: note: template bool std::operator==(const std::allocator&, const std::allocator&)/usr/include/c++/4.6/bits/stl_vector.h:1273:5: note: template bool std::operator==(const std::vector&, const std::vector&)/usr/include/c++/4.6/ext/new_allocator.h:123:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::new_allocator&, const __gnu_cxx::new_allocator&)/usr/include/c++/4.6/bits/stl_iterator.h:805:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)/usr/include/c++/4.6/bits/stl_iterator.h:799:5: note: template bool __gnu_cxx::operator==(const __gnu_cxx::__normal_iterator&, const __gnu_cxx::__normal_iterator&)
Edit 2016-04-29: gcc 5.3.0 got it a bit better: only 9300 bytes, longest line is 361 characters long...
Edit 2019-04-04: gcc 6.5.0: 11237 bytes, but gives some hints on the error, as in theses lines:
error.cpp:7:92: required from here/usr/include/c++/6/bits/predefined_ops.h:199:17: error: no match for ‘operator==’ (operand types are ‘std::vector’ and ‘const int’) { return *__it == _M_value; } ~~~~~~^~~~~~~~~~~Edit 2022-01-06: gcc 7.5.0 (Ubuntu 18.04): 11405 bytes, still no real clue on what happens, unfortunately (which could be something like, say, erroneous type 'int' as arg 3 for std::find(), expected type: 'std::vector<int>').
Oh, BTW, ratio error/code can even be increased by removing unnecessary stuff:
int main(){ int a; std::vector< std::vector <int> > v; std::find( v.begin(), v.end(), a );}