Array of pthread pointers

Question

I am trying to dynamically allocate a array of pthread pointers, but get this glibc error:

*** glibc detected *** ./test: realloc(): invalid next size: 0x00000000084d2010 ***

The code:

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

int main(int argc, char** argv) {
    pthread_t **threads;
    int i;

    for(i=1;i<100;i++) {
        threads = realloc(threads, sizeof(pthread_t*)*i);
        threads[i] = malloc(sizeof(pthread_t));
    }

   return EXIT_SUCCESS;
}

What am i doing wrong here?

md5 · Accepted Answer · 2012-10-25 15:06:50Z

2

You should initialize threads (emphasis is mine).

C11 (n1570), § 7.22.3.5 The realloc function

If ptr is a null pointer, the realloc function behaves like the malloc function for the specified size. Otherwise, if ptr does not match a pointer earlier returned by a memory management function, or if the space has been deallocated by a call to the free or realloc function, the behavior is undefined.

sizeof(pthread_t *) * i doesn't allocate enough memory to access to thread[i]. You have to allocate ((sizeof(pthread_t *) * (i + 1)).

edited Oct 25, 2012 at 15:06

answered Oct 25, 2012 at 15:00

md5

23.8k4 gold badges49 silver badges96 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Dave Rager Over a year ago

I just wonder why he's reallocating the array one element larger with every iteration instead of allocating the whole thing once before the for loop.

md5 Over a year ago

I don't understand either. But it seems to be a code extract.

user1774565 Over a year ago

Great, thanks. This is just an example of some other code where i don't necessarily know how many times i need to realloc.

Collectives™ on Stack Overflow

Array of pthread pointers

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related