c++ - Why is operator<< function between std::ostream and char a non-member function? -

when ran following program

#include <iostream>  int main() {    char c = 'a';    std::cout << c << std::endl;    std::cout.operator<<(c) << std::endl;     return 0; } 

i got output

a 97 

digging further @ http://en.cppreference.com/w/cpp/io/basic_ostream/operator_ltlt, noticed std::ostream::operator<<() not have overload has char argument type. function call std::cout.operator<<(a) gets resolved std::ostream::operator<<(int), explains output.

i assuming operator<< function between std::ostream , char declared elsewhere as:

std::ostream& operator<<(std::ostream& out, char c); 

otherwise, std::cout << a resolve std::ostream::operator<<(int).

my question why declared/defined non-member function? there known issues prevent being member function?

the set of inserters std::basic_ostream includes partial specializations inserting char, signed char, unsigned char , such basic_ostream<char, ...> streams. note these specializations made available basic_ostream<char, ...> streams only, not basic_ostream<wchar_t, ...> streams or streams based on other character type.

if move these freestanding templates main basic_ostream definition, become available specializations forms of basic_ostream. apparently, library authors wanted prevent happening.

i don't know why wanted introduce these specializations on top of more generic

template<class chart, class traits> basic_ostream<chart,traits>& operator<<(basic_ostream<chart,traits>&,                                         char); 

inserter, apparently had reasons (optimization?).

the same situation exists c-string inserters. in addition more generic inserter

template<class chart, class traits> basic_ostream<chart,traits>& operator<<(basic_ostream<chart,traits>&,                                         const char*); 

the library specification declares more specific

template<class traits> basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>&,                                        const char*); 

and on.