Question

I would like to resize the array when it reaches its max capacity. But error came up after i do ./a.out Please help me…

Error: a.out: malloc.c:3574: mremap_chunk: Assertion `((size + offset) & (mp_.pagesize-1)) == 0' failed.

code:

#include<stdio.h>
#include <stdlib.h>


int main(void)
{
  int cap=5;
  int *arr = malloc(cap*sizeof(int));
  FILE *f;

  if((f=fopen("/home/file.txt","r"))==NULL)
    printf("You cannot open");  

  while(fscanf(f, "%d", arr++)!=EOF)
  {
    index++;
    if(index==cap-1)
      arr = realloc(arr, (cap +=1) * sizeof(int));
  } 

  return 0;
}

Answer 1

You have arr++ in your loop condition. That means arr doesn’t point to the start of the allocated memory anymore when you call realloc(). That’s going to end up with the error you’re seeing.

Also:

1. Programming safety note:

   Don’t call realloc() in the form:

   foo = realloc(foo, bar);
   

   If an error occurs, foo will be set to NULL and you’ll leak the original allocation.

2. Nonidiomatic code note:

   (cap +=1) * sizeof(int)
   

   is a bit weird. Why not ++cap * sizeof(int)? Or better yet, do it on two lines rather than cramming it all into one.