template <class charT, class traits, class Alloc> basic_ostream<charT,traits>& operator<< (basic_ostream<charT,traits>& os, const basic_string<charT,traits,Alloc>& str);
Insert string into stream
Inserts the sequence of characters that conforms value of str into os.
This function overloads operator<< to behave as described in basic_ostream::operator<< for c-strings, but applied to basic_string objects.
The same as parameter os.
If some error happens during the output operation, the stream's badbit flag is set, and if the appropriate flag has been set with basic_ios::exceptions, an exception is thrown.
// inserting strings into output streams
std::string str = "Hello world!";
std::cout << str << '\n';
Unspecified, but generally linear in str's length.
Objects os is modified.
Basic guarantee: if an exception is thrown, both is and str end up in a valid state.