CODEWITHSUNDEEP
cpointersmemorydynamic
reyear
reyear

Reputation: 15

Why is the first value of the array being replaced?

I don't understand why the first value of my array is changed outside the inner while loop when the "i" increments correctly. Am I allocating memory in a way that messes something up? How do I go about correcting this issue?

int main(void) 
{
  int sizeArray = 5, sizeString = 10;
  FILE *fin = fopen("file.txt", "r");
  char ** arr = (char **) malloc(sizeArray * sizeof(char *));
  char line[1000];
  char *word;
  int i = 0;
  while(fgets(line, 100, fin) != NULL)
  {
    word = strtok(line, " ");
    while (i < 2)
    {
      arr[i] = (char *)malloc(sizeString * sizeof(char));
      arr[i] = word;
      printf("Inner print: %s\n\n",arr[0]);
      word = strtok(NULL, " ");
      i++;
    }

  }
    printf("This is the final arr[0] (outer print): %s",arr[0]);

}

file.txt reads as: 

First second.
Third! Fourth

The print from my console is as follows:

Inner print: First

Inner print: First

The final arr[0] (outer print): Third!

When I want the outer print to be: First

Upvotes: 0

Views: 77

Answers (2)

klutt
klutt

Reputation: 31296

You need to move int i = 0; inside the outer while loop. Or to the very least reset it to zero when the inner loop is done.

arr[i] = word is not how you copy strings in C. Have a look at strcpy, or even better, strncpy.

Performing arr[i] = word right after you have done arr[i] = (char *)malloc makes the malloc completely useless. The ONLY thing this accomplishes is to allocate space and then throw the pointer away, yielding a memory leak.

Upvotes: 0

1201ProgramAlarm
1201ProgramAlarm

Reputation: 32732

You allocate some memory with arr[i] = (char *)malloc(sizeString * sizeof(char));. You then immediately overwrite that pointer (leaking the memory) with arr[i] = word, so that arr[i] now points somewhere in the line buffer.

You need to copy the string pointed to by word into the buffer allocated for arr[i]:

strcpy_s(arr[i], sizeString * sizeof(char), word);

Upvotes: 1

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