Thread: Alright, how does one compare an element of argv with a literal string?

Originally Posted by skumarisation

Yeah this you can do by using"operator overloading" for which you need to write a function

Yeah, I know about operator loading, but I was hoping that the STL would already support using "==" or "!=" with two c-style strings. I don't know why the developers of the C++ STL haven't added it.

Originally Posted by laserlight

A catch here is that this compares the contents to check if they are not equal. Unless you have some special reason to use the c_str() member function here, it would really be simpler to do without it, e.g.,

Code:

if (myStdString == "--help")

Yeah, but the problem is "--help" is a c-style string, and "myStdString" is a std::string.
And the std::string type doesn't have a '==' operator.

Originally Posted by laserlight

They cannot, as one cannot overload on the built-in and pointer types without involving a class type.

Yeah...so why not involve a class type??

Originally Posted by Elysia

std::string DOES have an == operator.
The above code is perfectly legal.

string - C++ Reference

I don't see any '==' operator...

Originally Posted by laserlight

I see. Compile this program and tell us the compile error. If there is no compile error, run the program and tell us the output:

Code:

#include <iostream>
#include <string>

int main()
{
    std::string myStdString = "--help";
    if (myStdString == "--help")
    {
        std::cout << "Programmer_P";
    }
    else
    {
        std::cout << "laserlight";
    }
    std::cout << " is wrong." << std::endl;
}

Ok, fine then...I'm wrong.
I'll blame it on the writers of the string documentation reference article I just linked to at cplusplus.com.

Originally Posted by laserlight

That is precisely what I am telling you to do: involve a class type by constructing a std::string from one of the null terminated C-style strings.

I meant, why didn't the C++ STL developers involve a class type so they could overload the '==' operator?

Originally Posted by Programmer_P

string - C++ Reference

I don't see any '==' operator...

It may be hard to find a complete reference, but they exist, and so does operator==.

Originally Posted by the link

template <class charT, class traits, class Alloc>
bool operator==(const basic_string<charT, traits, Alloc>& s1,
const basic_string<charT, traits, Alloc>& s2)

Container String equality. A global function, not a member function.

template <class charT, class traits, class Alloc>
bool operator==(const charT* s1,
const basic_string<charT, traits, Alloc>& s2)

basic_string String equality. A global function, not a member function.

template <class charT, class traits, class Alloc>
bool operator==(const basic_string<charT, traits, Alloc>& s1,
const charT* s2)

basic_string String equality. A global function, not a member function.

Most references must not cover global functions introduced by the class.

Originally Posted by laserlight

Unfortunately for you, they did include those operators: comparison operators

Ok, but why didn't they put a link to that article on the main C++ string article, which I linked to?

Originally Posted by laserlight

They did, but I suppose you can fault them for not making it very prominent, heheh.

Yeh, its on the sidebar, but I meant why didn't they put it on the main part of the page.
Anyway, ok, I stand corrected...................