Thread: Playing around strlen :)

Code:

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

/*

The std's strlen algorithm:
From: Programming with lcc-win32 by Jacob Navia and Q Software Solutions GmbH

int strlen(char *str)
{
   char *p = str;

   while(*p != 0)
      p++;

   return p - str;
}

It will crash in both..

   char *test;
   printf("%d", strlen(test));

..and..

   char *test = NULL;
   printf("%d", strlen(test));

*/

//This is my modified std's strlen:

int strlen_mod(char *str)
{
   //Avoiding crashes by initializing string to NULL
   if(str == NULL) //a very simple fix
      return 0;

   char *p = str;

   while(*p != 0)
      p++;

   return p - str;
}


//They said passing by reference gives better performance:

int strlen_byref(char **str)
{
   if(*str == NULL)
      return 0;

   char *p = *str;

   while(*p != 0)
      p++;

   return p - *str;
}


//But, let's try something simple :) :

int strlen_simple(char **str)
{
   if(*str == NULL)
      return 0;

   int len = 0;

   while((*str)[len] != 0)
      len++;

   return len;
}

int main()
{
   char *str = "abcde";

   printf("%s\n\n", str);

   printf("strlen       : %d\n", strlen(str));
   printf("strlen_mod   : %d\n", strlen_mod(str));
   printf("strlen_byref : %d\n", strlen_byref(&str));
   printf("strlen_simple: %d\n", strlen_simple(&str));

   return 0;
}

Comments are welcome

I believe strlen() was written without a NULL check to make it faster, since most experienced programmers will do their own NULL checking (if there's a chance of it being NULL).
As for preventing the first crash, there's no portable way to check if a pointer has been initialized. You just have to assume the programmer knows better than that.