Iterating string with strchr in C

Question

If I have a string like char str [] = "hello;people;how;are;you" and use strchr(str,";") how can I take the N-th token of the string?

Prashant Negi · Answer 1 · 2016-09-21T08:43:30.087

3

Suppose you are storing the strchr in a char * ch

Then ch-str+1 will return you the position of the character that you looked for in strchr

Using a predefined substring function or defining a function of your own you can create a while loop like this :

i=0;
while(ch != NULL)
{
    printf("Your subsrting is : %s", substring_function(i,(ch-str+1)));
    i = ch-str+1;
    ch=strchr(ch+1,';');
}

edited Sep 21 '16 at 08:43

answered Sep 21 '16 at 08:30

Prashant Negi

348
2
14

Thanks for answering. I will use `strchr` , which has as argument the token, not the position i. – pole gar Sep 21 '16 at 08:38
You do not change `ch` in the loop, so it is an endless loop. – mch Sep 21 '16 at 08:39
@polegar this should work strchr is taking two arguments the pointer and the character you are looking for in the string – Prashant Negi Sep 21 '16 at 08:46

score 0 · Answer 2 · edited Sep 21 '16 at 16:32

0

OK, found a solution with strtok and I'd like to convert it using strchr. Tokenizer is static variable which contains the character for tokenizing. Any ideas?

static const char *a(const char *string,int tkn) {
    char *tokenized=strdup(string);
    char *token;
    token=strtok(tokenized, tokenizer);
    int i=0;
    while(token != NULL) {
      if (i == (tkn-1)) {
        break;
      }
      token = strtok(NULL, tokenizer);
      i++;
   }
   return token;
}

edited Sep 21 '16 at 16:32

chux - Reinstate Monica

143,097
13
135
256

answered Sep 21 '16 at 13:32

pole gar

53
9

This approach is a memory leak as the allocated `tokenized` is not certainly recoverable for a later `free()`. – chux - Reinstate Monica Sep 21 '16 at 16:34
Thanks a lot, I can add a free after all. Beyond that? – pole gar Sep 21 '16 at 16:44
"I can add a free after all" --> It is not that simple as code returns a pointer into allocated memory, but has lost the beginning of it. Suggest posting an answer that uses your "add a free" idea. – chux - Reinstate Monica Sep 21 '16 at 16:48
Delete strdup, use string directly in strtok with casting to char *. – pole gar Sep 21 '16 at 17:02
Using `strtok(string)` on a `const char *` is undefined behavior. Try coding it and see if your well enabled compiler warns. – chux - Reinstate Monica Sep 21 '16 at 17:34

Iterating string with strchr in C

2 Answers2