CODEWITHSUNDEEP
carrayspointers
User2423982IAm
User2423982IAm

Reputation: 3

C String into array

I need help with breaking a string into an array. I got it to work without storing the info and just printing the tokens. But for this prog, I need to store the tokens strtok made and use a binary search to do a strncmp with 2 elements each being from a different array.

./file "Example input: 'Cause I'm Batman"

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

int main(int argc, char *argv[])
{
  char delims[] = " ";
  char *result = NULL;

  int i = 1;
  int j = 0;

  char sent[1000];
  result = strtok(argv[1], delims);
  sent[0] = *result;
  while(result != NULL)
  {
    result = strtok(NULL, delims);
    sent[i] = *result;
    i++;
  }

  while(j < i)
  {
    printf(" %p\n", &sent[j]);
    j++; //Forgot to add it in first time around
  }
return 0;
}

Problem is I'm getting a segmentation fault and I can't seem to get it to store the tokens into an array and I don't understand why. Is it a pointer issue? Passing incompatible data types? Something else?

Edit: Wanted output: "Example" "input:" "'Cause" "I'm" "Batman"

Any help would be great.

Upvotes: 0

Views: 1315

Answers (3)

BLUEPIXY
BLUEPIXY

Reputation: 40145

fix like this

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

int main(int argc, char *argv[]){
    char delims[] = " ";
    char *result = NULL;
    int i = 0, j;
    char sent[1000];
    char *parray[32];//32 word

    strcpy(sent, argv[1]);//strtok destory string, argv[n] is read only.
    result = strtok(sent, delims);
    parray[i++] = result;
    while(NULL!= (result=strtok(NULL, delims))){
        parray[i++] = result;
    }

    for(j=0; j < i;++j)
        printf("%s\n", parray[j]);
    return 0;
}

Upvotes: 0

nurd_droid
nurd_droid

Reputation: 64

When strtok reaches '\0' NUL character in the string, it will return NULL pointer.

In your code 'result' is de-referenceed after making strtok(NULL, delims) call. As a result you will be de-referencing result without making a sanity check for its validity and will end up accessing NULL pointer.

Upvotes: 0

Some programmer dude
Some programmer dude

Reputation: 409176

In your case it's very easy to figure out what's causing the crash: You dereference the NULL pointer.

Think for a minute what will happen with the expression *result when result is NULL.

Also, this error would have taken you less than a minute to find if you used a debugger. When a program crashes, a programmers first instinct should always be to run the program in a debugger.

Upvotes: 1

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