Thread safe alternative of the strtok() function

strtoken.c

/*
 *  strtoken.c
 *
 *  Copyleft (C) 2015  Sun Dro (a.k.a. kala13x)
 *
 * This source is thread safe alternative of the strtok().
 * See usage of the get_token() below at main() function.
 */

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

/*
 * get_token() - Function breaks a string into a sequence of zero or more 
 * nonempty tokens. On the first call to get_token() func the string to be 
 * parsed should be specified in psrc. In each subsequent call that should 
 * parse the same string, psrc must be NULL. The delimit argument specifies 
 * a set of bytes that delimit the tokens in the parsed string. Functions 
 * return a pointer to the next token, or NULL if there are no more tokens.
 */
char *get_token(char *psrc, const char *delimit, void *psave) 
{
    static char sret[512];
    register char *ptr = psave;
    memset(sret, 0, sizeof(sret));

    if (psrc != NULL) strcpy(ptr, psrc);
    if (ptr == NULL) return NULL;

    int i = 0, nlength = strlen(ptr);
    for (i = 0; i < nlength; i++)
    {
        if (ptr[i] == delimit[0]) break;
        if (ptr[i] == delimit[1]) 
        {
            ptr = NULL;
            break;
        }
        sret[i] = ptr[i];
    }
    if (ptr != NULL) strcpy(ptr, &ptr[i+1]);

    return sret;
}

int main(int argc, char *argv[]) 
{
    char string[32];
    char saveptr[32];
    char delimit[2] = {':', '\0'};

    strcpy(string, "first:second:third");

    char *ptr = get_token(string, delimit, &saveptr);
    printf("1: %s\n", ptr);

    ptr = get_token(NULL, delimit, &saveptr);
    printf("2: %s\n", ptr);

    ptr = get_token(NULL, delimit, &saveptr);
    printf("3: %s\n", ptr);

    return 0;
}