C++: How to make comparison function for char arrays?

Is this possible? i get weird error message when i put char as the type:

inline bool operator==(const char *str1, const char *str2){
    // ...
}

Error message: error C2803: 'operator ==' must have at least one formal parameter of class type ... which i dont understand at all.

I was thinking if i could directly compare stuff like:

const char *str1 = "something";
const char *str2 = "something else";
const char str3[] = "lol"; // not sure if this is same as above

and then compare:

if(str1 == str2){
   // ...
}

etc.

But i also want it to work with:

char *str = new char[100];

and:

char *str开发者_开发问答 = (char *)malloc(100);

I am assuming every char array i use this way would end in NULL character, so the checking should be possible, but i understand it can be unsafe etc. I just want to know if this is possible to do, and how.

It is not possible. As your compiler points out, you cannot overload this operator for primitive data types. At least one side of the comparison must be non-primitive for the overload to be possible.

In the same sense, you cannot derive a new class from a primitive data type (to add functionality to it).

You are attempting to compare two pointers.

const char* str1 = "string1";
const char* str2 = "string1";

if(str1 == str2) // never true, str1 is not the same pointer as str2
{
};

But, you've provided the C++ tag, so you should be using std::string:

#include <string>

std::string str1 = "string1";
std::string str2 = "string1";

if(str1 == str2)  // yes!  std::string overloads operator ==
{
}

Pointers are built-in types. There are built-in comparison operators for them already, you cannot override them. Just use std::string.

You most certainly, totally can write your own comparison function, and in fact it's one of the most basic things to do. I have no idea why someone would say that you can't. You just can't call it operator =. Here it is (untested):

int my_strcmp(char const* s1, char const* s2)
{
  for(;*s1 == *s2 && *s1; ++s1,++s2);

  return *s1 - *s2;
}

...
if (!my_strcmp(str1, str2)) // they're ==.

Use strcmp() to compare chars: It works on char pointers char * and char arrays char [ ] .

#include <string.h>
#include <stdio.h>

char *string_Char_pointer1 = {"2012-12-06 14:28:51"};
char *string_Char_pointer2 = {"1911-12-06 14:28:51"};

char string_Char_Array1[] = "2012-12-06 14:28:51";
char string_Char_Array2[] = "1911-12-06 14:28:51";

int main( void )
{
   char tmp[20];
   int result;

   printf( "Comparing  string_Char_pointer..\n\n\n");

   printf( "Compared strings:\n   %s\n   %s\n\n\n", string_Char_pointer1, string_Char_pointer2 );
   result = strcmp( string_Char_pointer1, string_Char_pointer2 );

   if( result > 0 )        strcpy( tmp, "greater than" );
   else if( result < 0 )   strcpy( tmp, "less than" );
   else    strcpy( tmp, "equal to" );

   printf( "   strcmp:   String 1 is %s string 2\n\n", tmp );

   printf( "\n\nComparing string_Char_Array..\n\n");

   printf( "Compared strings:\n   %s\n   %s\n\n\n", string_Char_Array1, string_Char_Array2 );
   result = strcmp( string_Char_pointer1, string_Char_pointer2 );

   if( result > 0 )        strcpy( tmp, "greater than" );
   else if( result < 0 )   strcpy( tmp, "less than" );
   else    strcpy( tmp, "equal to" );




   return 0;
}

Decided that my comment would be better as an answer, you should use the standard string functions for this (strncmp, strncat, etc).

Edit: As pointed out in another answer, you can't do the overload. But in the case of the char arrays and char pointers you should use the standard library functions.