Difference between operator<< and write function?

Question

I wonder what is the difference between std::basic_ostream<CharT,Traits>::operator<< and std::basic_ostream<CharT,Traits>::write. What about performance?

#include <iostream>
#include <string>

int main()
{
    std::string tempMsg;
    tempMsg.reserve( 100 );
    tempMsg += "This is a string";

    std::cout.write( tempMsg.data( ), tempMsg.size( ) ).write( "\n", 1 );
    std::cout << tempMsg << '\n';
}

They both print the same string. But what are the advantages of each of them?

Answer 1

The function allows to specify the number of characters to be outputted for a character array.

For example of you have declaration

const char *s = "Hello World!";

and want to output only the word "Hello" from the string literal then you can write

std::cout.write( s, 5 );

If you will write

std::cout << s;

then the whole string literal will be outputted.

Thus using the function you can output any part of a character array as for example

std::cout. write( s + 6, 2 ) << 'w' << s + 11 << '\n';

As for the performance then there is no difference or the difference is insignificant. What is important is the functionality.