CODEWITHSUNDEEP
cstringstrtok
mackesmilian
mackesmilian

Reputation: 123

strtok is causing a Segmentation Fault

I have to get the third word in a string and wanted to use strtok. Now, the first printf works but after that I get a Seg Fault. So tokenizedString = strtok(NULL, " "); must be causing the issue, right?

Just for context: I'm looking for the third word in a string and there can be as many spaces as possible between the words.

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

char *tokenizeString(char *userCommand)
{
  char *tokenizedString;
  int counterForToken;
  tokenizedString = strtok(userCommand, " ");
  for(counterForToken = 0; counterForToken != 3; counterForToken++)
  {
    printf("%s\n", tokenizedString);
    tokenizedString = strtok(NULL, " ");
    if(tokenizedString == NULL)
    {
        break;
    }
  }
  printf("%s\n", tokenizedString);
  return tokenizedString; 
}

int main(void)
{
  char userCommand[255] = {0};
  fgets(userCommand, sizeof(userCommand), stdin);
  tokenizeString(userCommand);
}

Upvotes: 0

Views: 141

Answers (1)

StoryTeller - Unslander Monica
StoryTeller - Unslander Monica

Reputation: 170074

Now, the first printf works but after that I get a Seg Fault. So tokenizedString = strtok(NULL, " "); must be causing the issue, right?

No, that is very poor correlation. The issue is in fact in the second call to printf. You can pass it tokenizedString when tokenizedString == NULL. The format specified %s is specified to expect a valid pointer to the first character of a zero terminated array of characters. Passing it NULL is illegal and leads to undefined behavior (causing a crash for instance). The fix is simple: check for a null pointer value. And the same applies to the first iteration of the loop, of course

char *tokenizeString(char *userCommand)
{
  char *tokenizedString;
  int counterForToken;
  tokenizedString = strtok(userCommand, " ");
  for(counterForToken = 0; counterForToken != 3 && tokenizedString != NULL; counterForToken++)
  {
    printf("%s\n", tokenizedString);
    tokenizedString = strtok(NULL, " ");
  }
  if(tokenizedString != NULL)
    printf("%s\n", tokenizedString);
  return tokenizedString; 
}

Upvotes: 1

Related Questions