Compare std::ostream to see if it is std::cout ("no match for 'operator=='")

Question

The functionality of this function is that it will output(to terminal or file depending on the type of ostream& os object passed as a parameter to it) the MyString data (the C-string representation held within m_buffer). I am receiving a compiler error that states that "no match for 'operator=='", specifically in the part of the code that states "if(os == std::cout)" Any suggestions? Thank you!

//in header file
friend std::ostream & operator<<(std::ostream & os, const MyString & myStr);

//in cpp file
bool MyString::operator==(const MyString & other)const{
if(strcmp(m_buffer,other.m_buffer) == 0){
    return true;
}else if (strcmp(m_buffer,other.m_buffer) != 0){
    return false;
}
}

std::ostream& operator<<(std::ostream& os, const MyString& myStr){
  if(os == std::cout){
  os << myStr.m_buffer << std::endl;
}
}

Answer 1

You can compare the addresses:

if (&os == &std::cout) {
  os << myStr.m_buffer << std::endl;
}

it will output(to terminal or file depending on the type of ostream& os object passed as a parameter to it)

os can also be a file stream since file streams also derived from std::ostream / std::istream . So writing to os will write to the terminal or file that the stream represents so there's really no need for the condition.

Answer 2

Because the std::ostream class aka std::basic_ostream < char > doesn't provide by any means comparison operators, and in general does not make sense to compare streams.

That said, a possible solution ( based on this answer ) is this

if( std::addressof( os ) == std::addressof( std::cout ) )
  {
    os << myStr.m_buffer << std::endl;
  }

--

References:

https://en.cppreference.com/w/cpp/io/basic_ostream

https://en.cppreference.com/w/cpp/memory/addressof