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How strtok library function is implemented ?

+2 votes
How strtok library function is implemented ?
posted Jun 13, 2015 by Harshita

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2 Answers

+2 votes

its a c library function which is used to tokenize a given string based on the token character provided.
its prototype is char *strtok(char *str, const char*tok).

char a[] = "This";
char *tok = strtok(a, '-');
     printf("%s\n" tok);
     tok = strtok(NULL, '-');


This is

Basically strtok() function maintains a local static reference, which points to the next token in the string, when we pass a null to strtok() its uses that internal reference. This is the reason strtok is neither re-entrant nor thread safe. as you pass the new reference to strtok() that old internal reference gets overwrite.

answer Jun 13, 2015 by Prakash Singh
+1 vote

This is my implementation, does not require any explanation -

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

char* my_strtok(char* s, char* delm)
    static int currIndex = 0;
    char *W = (char *)malloc(sizeof(char)*100);
    int i = currIndex, k = 0, j = 0;

    if(!s || !delm || s[currIndex] == '\0')
      return NULL;

    while (s[i] != '\0'){
        j = 0;
        while (delm[j] != '\0'){
            if (s[i] != delm[j])
                W[k] = s[i];
                goto It;

    W[i] = 0;
    currIndex = i+1;
    return W;

int main(void)
  char s[100] = "I am JameBond 007";
  char delm[] = " ";
  char *str = my_strtok(s, delm);
    printf("%s\n", str);
    str = my_strtok(s, delm);
  return 0;
answer Jun 13, 2015 by Pardeep Kohli
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