/**
 * 
 * Implementation and example usage for string tokenization,
 * that is to say, splitting a string into pieces based
 * on a character.  This implementation follows, not quite
 * perfectly, strtok in string.h
 * 
 * @author gtowell
 * Created: Sep 2019
 * Modified: Mar 2021
 * **/

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

#ifndef NULL
#define NULL (void *) 0
#endif

/** 
 * Used by strtok to hold the last place read from the target string
 * **/
char * mystrtok_lastp;

/**
 * Tokenize a string.  First call will return first part of string up to token
 * Note that this function modifies the passed string!
 * @param string the string to tokenize  Should only be non-NULL on first call.
 * @param teh character to split up the string 
 * @return a pointer to a part of the string
 * **/
char * mystrtok(char * string, char token) {
    if (string!=NULL) {
	    mystrtok_lastp=string;
    }
    else {
	    if (mystrtok_lastp==NULL)
	        return NULL;	
	    mystrtok_lastp++;
    }
    char *holdp=mystrtok_lastp;
    char *nptr = mystrtok_lastp;
    while (*nptr!=token && *nptr!='\0') {
    	nptr++;
    }
    if (*nptr=='\0') {
    	mystrtok_lastp=NULL;
    }
    else {
	    mystrtok_lastp=nptr;
	    *nptr='\0';
    }
    return holdp;
}

/**
 * Example of strtok usage.
 * Uses command line for input
 * cl1 should be a single character to split a string on e.g. ,
 * cl2 should be the string to be split.  e.g., "the,box,is,a,pen"
 * **/
int main(int argc, char *argv[])
{
    char splitter = argv[1][0];
    char *string = argv[2];
    char *splitPiece;
    printf("String  \"%s\" is split into tokens using a single char \"%c\":\n", string, splitter);
    splitPiece = mystrtok(string, splitter); // get first token
    printf("%s\n", splitPiece);
    // get subsequent tokens  -- NOTE USE OF NULL -- cannot split two string at same time
    while (NULL != (splitPiece = mystrtok(NULL, splitter))) { 
        printf("%s\n", splitPiece);
    }
}