invalid pointer from trying to use realloc for an array of structs in c

Question

My program compiles but I am not working with pointers and realloc correctly. I have tried looking at other examples but I can't seem to translate it to my own program. The point of the program is to read in words from a file and increment the count if they appear more than once. Once the array of structs goes over my base (5), I want to realloc space, copy the array over and then add the next word.

Any help would be greatly appreciated!

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define BASE 5
#define MAX 50

typedef char *string;

 struct wordCount 
 {
 string word; 
 unsigned int count;
  }; 

 int main (void)
 {  
unsigned int i; 
unsigned int incremented; 
unsigned int j; 
char temp [40];  
struct wordCount wordArray[BASE]; 
struct wordCount *holder;  
FILE *infile;   

j = 0; 
infile = fopen("input.txt","r");
while (fscanf(infile, "%s", temp) == 1) { 
    incremented = 0; 
    for (i = 0; i < j; i++){
        if(strcmp(temp,wordArray[i].word) == 0){
            wordArray[i].count++;
            incremented++; 
        } 
     }
     if (incremented == 0){
        if (j<BASE){     
            wordArray[j].word = (char *)malloc((strlen(temp)+1) * 
                               sizeof(char));
            strcpy(wordArray[j].word,temp); 
            wordArray[j].count = 1; 
            j++;  
        } else {
          holder = realloc(wordArray, sizeof(wordArray) +1);
          *wordArray = *holder;
          wordArray[j].word = (char *)malloc((strlen(temp)+1) * sizeof(char));
          strcpy(wordArray[j].word,temp); 
          wordArray[j].count = 1; 
          j++; 
        }
     }
}

fclose(infile);

/* bring in next file*/
/*delete du plicates */ 
/*sort*/ 

for (i = 0; i < j; i++) {
    printf("%s ", wordArray[i].word);
    printf("%d\n", wordArray[i].count); 
}
/* and when done:*/ 
   for(i = 0; i < j; i++){
      free(wordArray[i].word);
}

return 0; 
 }

Mike · Accepted Answer · 2013-04-30 17:04:31Z

3

Here's the most obvious place you're going wrong:

holder = realloc(wordArray, sizeof(wordArray) +1);

Note this line from the man page of realloc():

void *realloc(void *ptr, size_t size);
...
Unless ptr is NULL, it must have been returned by an earlier call to malloc(), calloc() or realloc().

Your wordArray is a statically allocated array, it was not dynamically allocated via malloc() or friends.

answered Apr 30, 2013 at 17:04

Mike

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