#include 
#include 
int my_strlen(const char* str)
{
  assert(str);
  int count = 0;
  while (*str) {
  count++;
  str++;
  }
  return count;
}
int main()
{
  char arr[] = "abcdef";
        int len = my_strlen(arr);
  printf("%d\n", len);
  return 0;
}

#include 
#include 
size_t my_strlen(const char* str)
{
  assert(str);
  const char* eos = str;
  while (*eos++);
  return(eos - str - 1);
}
int main()
{
  char arr[] = "abcdef";
  printf("%d\n", my_strlen(arr));
  return 0;
}

/***
*strlen.c - contains strlen() routine
*
*       Copyright (c) Microsoft Corporation. All rights reserved.
*
*Purpose:
*       strlen returns the length of a null-terminated string,
*       not including the null byte itself.
*
*******************************************************************************/
#include 
#include 
#pragma function(strlen)
/***
*strlen - return the length of a null-terminated string
*
*Purpose:
*       Finds the length in bytes of the given string, not including
*       the final null character.
*
*Entry:
*       const char * str - string whose length is to be computed
*
*Exit:
*       length of the string "str", exclusive of the final null byte
*
*Exceptions:
*
*******************************************************************************/
size_t __cdecl strlen (
        const char * str
        )
{
        const char *eos = str;
        while( *eos++ ) ;
        return( eos - str - 1 );
}
size_t ：无符号整型（unsigned int）
__cdecl ：函数调用约定