关于string（basic_string)类
c里的string类没有"+"操作符，所有无法执行c=a+b（变量都是string类型）
但是为什么c++的这个string（basic_string)同样找不到"+"操作符的重载，却可以执行"+"操作符呢？

摘自msdn里的basic_string说明：
basic_string
allocator_type append assign at basic_string begin c_str capacity char_type compare const_iterator const_pointer const_reference const_reverse_iterator copy data difference_type empty end erase find find_first_not_of find_first_of find_last_not_of find_last_of get_allocator insert iterator length max_size npos operator+= operator= operator[] pointer rbegin reference rend replace reserve resize reverse_iterator rfind size size_type substr swap traits_type value_type

[解决办法]
c里面没有string.
c++里面重载的全局的+号，但不是basic_string类成员函数，所以msdn就没有显示出来。
具体代码你可以看<string>文件,里面有重载的

template<class _Elem,
class _Traits,
class _Alloc> inline
basic_string<_Elem, _Traits, _Alloc> __CLRCALL_OR_CDECL operator+(
const basic_string<_Elem, _Traits, _Alloc>& _Left,
const basic_string<_Elem, _Traits, _Alloc>& _Right)
{// return string + string
return (basic_string<_Elem, _Traits, _Alloc>(_Left) += _Right);
}

File: "C:\Program Files\Microsoft Visual Studio 10.0\VC\crt\src\string" 34 occurrences found on 34 lines
    15:         // basic_string TEMPLATE OPERATORS
    19:     basic_string<_Elem, _Traits, _Alloc> operator+(
    33:     basic_string<_Elem, _Traits, _Alloc> operator+(
    47:     basic_string<_Elem, _Traits, _Alloc> operator+(
    61:     basic_string<_Elem, _Traits, _Alloc> operator+(
    75:     basic_string<_Elem, _Traits, _Alloc> operator+(
    89:     basic_string<_Elem, _Traits, _Alloc> operator+(
    99:     basic_string<_Elem, _Traits, _Alloc> operator+(
   109:     basic_string<_Elem, _Traits, _Alloc> operator+(
   123:     basic_string<_Elem, _Traits, _Alloc> operator+(
   133:     basic_string<_Elem, _Traits, _Alloc> operator+(
   143:     basic_string<_Elem, _Traits, _Alloc> operator+(
   153:     basic_string<_Elem, _Traits, _Alloc> operator+(
   163:     bool operator==( 
 
   173:     bool operator==(
   183:     bool operator==(
   193:     bool operator!=(
   203:     bool operator!=(
   213:     bool operator!=(
   223:     bool operator<(
   233:     bool operator<(
   243:     bool operator<(
   253:     bool operator>(
   263:     bool operator>(
   273:     bool operator>(
   283:     bool operator<=(
   293:     bool operator<=(
   303:     bool operator<=(
   313:     bool operator>=(
   323:     bool operator>=(
   333:     bool operator>=(
   344:     basic_istream<_Elem, _Traits>& operator>>(
   458:     basic_istream<_Elem, _Traits>& operator>>(
   489:     basic_ostream<_Elem, _Traits>& operator<<(