template<typename T> void swap(T &a, T &b) {
	T tmp = a; a = b; b = tmp;
}

这段代码当和结构体的重载运算符的 sort 共同使用的时候就会报错，信息如下：

39	0	C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\bits\char_traits.h	In file included from C:/Program Files (x86)/Dev-Cpp/MinGW64/lib/gcc/x86_64-w64-mingw32/4.9.2/include/c++/bits/char_traits.h
40		C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\ios	                 from C:/Program Files (x86)/Dev-Cpp/MinGW64/lib/gcc/x86_64-w64-mingw32/4.9.2/include/c++/ios
38		C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\istream	                 from C:/Program Files (x86)/Dev-Cpp/MinGW64/lib/gcc/x86_64-w64-mingw32/4.9.2/include/c++/istream
38		C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\sstream	                 from C:/Program Files (x86)/Dev-Cpp/MinGW64/lib/gcc/x86_64-w64-mingw32/4.9.2/include/c++/sstream
45		C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\complex	                 from C:/Program Files (x86)/Dev-Cpp/MinGW64/lib/gcc/x86_64-w64-mingw32/4.9.2/include/c++/complex
38		C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\ccomplex	                 from C:/Program Files (x86)/Dev-Cpp/MinGW64/lib/gcc/x86_64-w64-mingw32/4.9.2/include/c++/ccomplex
52		C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\x86_64-w64-mingw32\bits\stdc++.h	                 from C:/Program Files (x86)/Dev-Cpp/MinGW64/lib/gcc/x86_64-w64-mingw32/4.9.2/include/c++/x86_64-w64-mingw32/bits/stdc++.h
1		D:\OI\test.cpp	                 from D:\OI\test.cpp
C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\bits\stl_algobase.h	In instantiation of 'void std::iter_swap(_ForwardIterator1, _ForwardIterator2) [with _ForwardIterator1 = edg*; _ForwardIterator2 = edg*]':
84	34	C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\bits\stl_algo.h	required from 'void std::__move_median_to_first(_Iterator, _Iterator, _Iterator, _Iterator, _Compare) [with _Iterator = edg*; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
1921	13	C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\bits\stl_algo.h	required from '_RandomAccessIterator std::__unguarded_partition_pivot(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = edg*; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
1952	62	C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\bits\stl_algo.h	required from 'void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size, _Compare) [with _RandomAccessIterator = edg*; _Size = long long int; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
1969	11	C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\bits\stl_algo.h	required from 'void std::__sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = edg*; _Compare = __gnu_cxx::__ops::_Iter_less_iter]'
4685	72	C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\bits\stl_algo.h	required from 'void std::sort(_RAIter, _RAIter) [with _RAIter = edg*]'
114	32	D:\OI\test.cpp	required from here
148	22	C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\bits\stl_algobase.h	[Error] call of overloaded 'swap(edg&, edg&)' is ambiguous
148	22	C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\bits\stl_algobase.h	[Note] candidates are:
59	0	C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\bits\stl_pair.h	In file included from C:/Program Files (x86)/Dev-Cpp/MinGW64/lib/gcc/x86_64-w64-mingw32/4.9.2/include/c++/bits/stl_pair.h
64		C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\bits\stl_algobase.h	                 from C:/Program Files (x86)/Dev-Cpp/MinGW64/lib/gcc/x86_64-w64-mingw32/4.9.2/include/c++/bits/stl_algobase.h
39		C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\bits\char_traits.h	                 from C:/Program Files (x86)/Dev-Cpp/MinGW64/lib/gcc/x86_64-w64-mingw32/4.9.2/include/c++/bits/char_traits.h
40		C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\ios	                 from C:/Program Files (x86)/Dev-Cpp/MinGW64/lib/gcc/x86_64-w64-mingw32/4.9.2/include/c++/ios
38		C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\istream	                 from C:/Program Files (x86)/Dev-Cpp/MinGW64/lib/gcc/x86_64-w64-mingw32/4.9.2/include/c++/istream
38		C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\sstream	                 from C:/Program Files (x86)/Dev-Cpp/MinGW64/lib/gcc/x86_64-w64-mingw32/4.9.2/include/c++/sstream
45		C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\complex	                 from C:/Program Files (x86)/Dev-Cpp/MinGW64/lib/gcc/x86_64-w64-mingw32/4.9.2/include/c++/complex
38		C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\ccomplex	                 from C:/Program Files (x86)/Dev-Cpp/MinGW64/lib/gcc/x86_64-w64-mingw32/4.9.2/include/c++/ccomplex
52		C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\x86_64-w64-mingw32\bits\stdc++.h	                 from C:/Program Files (x86)/Dev-Cpp/MinGW64/lib/gcc/x86_64-w64-mingw32/4.9.2/include/c++/x86_64-w64-mingw32/bits/stdc++.h
1		D:\OI\test.cpp	                 from D:\OI\test.cpp
166	5	C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++\bits\move.h	[Note] void std::swap(_Tp&, _Tp&) [with _Tp = edg]
35	27	D:\OI\test.cpp	[Note] void swap(T&, T&) [with T = edg]