I'm trying to implement a strlen function in C with recursion and for some reason it's returning a 4 times bigger value than expected.

int *strlen(char *s)
{
   if(*s == '\0')
       return 0;
   else
       return 1   strlen(s 1);
}

Interestingly, when I change the type return of the function to "char", I get the desired result. I don't understand why, it should return an int anyways. I copied this code from a book, it should be right.

CodePudding user response：

Your function returns a pointer. On your system, an int is 4 bytes. Pointer arithmetic means that adding 1 to an int pointer increases its value by 4. When you change the return value to char * it "works" because char is 1 byte, so pointer arithmetic means that adding 1 to a char pointer increments its value by 1.

Your function does not need to return a pointer at all.

int strlen(char *s)
{
  if (*s == '\0')
      return 0;
  else
      return 1   strlen(s 1);
}

It'd be even more appropriate to have it return size_t than int.

CodePudding user response：

1. strlen should return size_t not int.
2. You return a pointer instead of an integer.

size_t mystrlen(const char *str)
{
    return *str ? 1   mystrlen(str   1) : 0;
}

int main(int argc, const char *argv[])
{
    printf("%zu\n", mystrlen("Hello"));
}

I copied this code from a book, it should be right

If they want you to return pointer to the integer then maybe they want something weird like this:

int *mystrlen(const char *str)
{
    static int first = 1;
    static int size = 0;
    if(first) {size = 0; first = 0;}

    if(*str)
    {
        size  ;
        mystrlen(str   1);
    }
    else
    {
        first = 1;
    }
    return &size;
}

int main(int argc, const char *argv[])
{
    printf("%d\n", *mystrlen("Hello"));
    printf("%d\n", *mystrlen(" World"));
}