C++ does not use variables to find string length strlen function

In this paper, an example of C++ without using variables to calculate the string length strlen function. Share with you for your reference. The specific implementation method is as follows:

1, strlen source code implementation:

size_t strlen(const char *str)
//Strlen doesn't make memory invalid judgments. If it's NULL, it's core.
{
    const char *eos=str;
    while(*eos++);
    return (eos-str-1);
}

2. Regular test questions will require no additional variables to achieve strlen function:

Implement a:

int strlen(const char *str)
{
   if('0'==*str)
       return 0;
   else
       return strlen(str+1)+1;
}

To realize two:

int strlen(const char *str)
{
   return *str?(strlen(str+1)+1):0;
}

Hope that the article described in the C++ programming to help you.