Solved

allocating memory for a data structure and accessing it

Posted on 2007-11-23
5
170 Views
Last Modified: 2010-04-15
I get an access violation from the below code.
Can't figure it out and would appreciate some tips.

Thanks!

typedef struct associativity

   {

   int vb; /* valid bit */

   int tag;

   } assoc_t;
 

typedef struct cache_line

   {

   assoc_t *assoc;

   int     *replacement;

   } cache_line_t;
 

cache_line_t *cache=NULL;
 

  numblocks = 64;

  cache_blocksize = 1;

  if ((cache = malloc(numblocks * 2 * sizeof(int))) == NULL) {

    (void)fprintf(stderr, "ERROR: Malloc failed");

    (void)exit(EXIT_FAILURE);    /* or return EXIT_FAILURE; */

  }

   /* for each cache line, allocate the assoc arrays */

    

    if ((assoc = malloc(numblocks * cache_blocksize * 2 * sizeof(int))) == NULL) {

    (void)fprintf(stderr, "ERROR: Malloc failed");

    (void)exit(EXIT_FAILURE);    /* or return EXIT_FAILURE; */

 

  }
 

    / *    initialize   * /

    

    j=0;

    i=0;

    for (j=0;j<numblocks;j++){

    

        for (i=0;i<cache_blocksize;i++){

            cache[j].assoc[i].vb = 0;

            cache[j].assoc[i].tag = 0;

    }

   }

}

Open in new window

0
Comment
Question by:d2fox
  • 3
  • 2
5 Comments
 
LVL 53

Expert Comment

by:Infinity08
Comment Utility
First of all, you'd better change this :

          if ((cache = malloc(numblocks * 2 * sizeof(int))) == NULL) {

into :

          if ((cache = malloc(numblocks * sizeof(cache_line_t))) == NULL) {

and the same for :

          if ((assoc = malloc(numblocks * cache_blocksize * 2 * sizeof(int))) == NULL) {

which becomes :

          if ((assoc = malloc(numblocks * cache_blocksize * sizeof(assoc_t))) == NULL) {



You also probably want to put the second malloc in a loop that loops over the previously allocated cache_line_t's, and allocates their respective alloc members. Because otherwise these lines will cause the access violation you saw :

            cache[j].assoc[i].vb = 0;
            cache[j].assoc[i].tag = 0;



0
 
LVL 55

Expert Comment

by:Jaime Olivares
Comment Utility
I think this line:
     if ((cache = malloc(numblocks * 2 * sizeof(int))) == NULL) {
should be:
     if ((cache = malloc(numblocks * sizeof(cache_line_t))) == NULL) {
 
0
 
LVL 55

Expert Comment

by:Jaime Olivares
Comment Utility
You are assuming that the struct have the same size of 2 integers, but this not always is true.
Anyway this kind of calculation is unnecessary.
0
 
LVL 53

Accepted Solution

by:
Infinity08 earned 250 total points
Comment Utility
Or your modified code would be :

typedef struct associativity {

  int vb; /* valid bit */

  int tag;

} assoc_t;

 

typedef struct cache_line {

  assoc_t *assoc;

  int     *replacement;

} cache_line_t;

 

cache_line_t *cache=NULL;

 

  numblocks = 64;

  cache_blocksize = 1;
 

  if ((cache = malloc(numblocks * sizeof(cache_line_t))) == NULL) {

    (void)fprintf(stderr, "ERROR: Malloc failed");

    (void)exit(EXIT_FAILURE);    /* or return EXIT_FAILURE; */

  }
 

  /* for each cache line, allocate the assoc arrays */

  for (j = 0; j < numblocks; ++j) {

    if ((cache[j].assoc = malloc(numblocks * cache_blocksize * sizeof(assoc_t))) == NULL) {

      (void)fprintf(stderr, "ERROR: Malloc failed");

      (void)exit(EXIT_FAILURE);    /* or return EXIT_FAILURE; */

    }

  }
 

  / *    initialize   * /

  for (j = 0; j < numblocks; ++j) {

    for (i = 0; i < cache_blocksize; ++i) {

      cache[j].assoc[i].vb = 0;

      cache[j].assoc[i].tag = 0;

    }

  }

}

Open in new window

0
 
LVL 53

Expert Comment

by:Infinity08
Comment Utility
Oh, and this :

      / *    initialize   * /

is not a valid comment. The /* and */ can't contain spaces !! So it has to be :

      /*    initialize   */
0

Featured Post

Highfive + Dolby Voice = No More Audio Complaints!

Poor audio quality is one of the top reasons people don’t use video conferencing. Get the crispest, clearest audio powered by Dolby Voice in every meeting. Highfive and Dolby Voice deliver the best video conferencing and audio experience for every meeting and every room.

Join & Write a Comment

This tutorial is posted by Aaron Wojnowski, administrator at SDKExpert.net.  To view more iPhone tutorials, visit www.sdkexpert.net. This is a very simple tutorial on finding the user's current location easily. In this tutorial, you will learn ho…
This is a short and sweet, but (hopefully) to the point article. There seems to be some fundamental misunderstanding about the function prototype for the "main" function in C and C++, more specifically what type this function should return. I see so…
The goal of this video is to provide viewers with basic examples to understand and use structures in the C programming language.
Video by: Grant
The goal of this video is to provide viewers with basic examples to understand and use nested-loops in the C programming language.

743 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

18 Experts available now in Live!

Get 1:1 Help Now