How does the C++ compiler interpret the == operator?

   std::string somestring;
    /*...*/
    if("STRING_LITERAL" == somestring)
    std::cout << "Strings are Equal" << std::endl;

In the sampl开发者_运维问答e code above, how does a C++ compiler interpret the == operator? As the == operator overloaded by the string class?

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If you're using std::string then you should have #included the <string> header. Assuming this is the case then the operator== selected should be the non-member template function from <string> with appropriate template parameters deduced. (ISO/IEC 14882:2003 21.3.7.2 [lib.string::operator==])

template<class charT, class traits, class Allocator>
bool operator==(const charT* lhs,
    const basic_string<charT,traits,Allocator>& rhs);

The std::string class (strictly class template specialization) doesn't contain any member overloads for operator==.

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Yes. The operator== is implemented as a free standing function, that's why the positioning is irrelevant. It could be

bool operator==(const string& str1, const char* str2){
  // ...
}

or

bool operator==(const char* str1, const string& str2){
  // ...
}

or even a simple

bool operator==(const string& str1, const string& str2){
  // ...
}

With an automatic conversion from char const* to string, as the relevant constructor of std::string is non-explicit.

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There is an overload of operator== that does the right thing:

template <class charT, class traits, class Allocator>
bool operator==(const charT* lhs,
                const basic_string<charT, traits, Allocator>& rhs);

You can find it in 21.3 §1 of the C++0x FDIS on page 635.

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From http://www.cplusplus.com/reference/string/operators/ , these overloads are defined:

bool operator== ( const string& lhs, const string& rhs );
bool operator== ( const char* lhs, const string& rhs );
bool operator== ( const string& lhs, const char* rhs );

Note that these are global functions, not methods of the string class (but they'll be implemented using string::compare().