problems with malloc

[antoroma]

Dear members, I am new to this forum and to the C language. I have stumble to this memory allocation problem and I shave spent the last 10 hours trying to find why this piece of code does not work (I compile with Dev C++): as I try to set the vectors Value_old and Value_new to zero the code crushes. I hope you guys can help me on this. Thanks much.

AntoRoma

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

#define TOTAL_LENGTH   170 
#define POPSIZE               10
#define MEM1 (2 * POPSIZE * sizeof(int *))
#define MEM2 (2 * POPSIZE * TOTAL_LENGTH * sizeof(int))
#define MEM (MEM1 + MEM2)

int main()
{ 
  int i,j;
  int **Value_old, **Value_new;
  double *ptr;
  
  ptr = malloc(MEMSIZE);
  if(!ptr) exit(-1);
  
  Value_old = (int **)  ptr;
  Value_new = (int **) (ptr + POPSIZE * sizeof(int *));
  for(i = 0; i < POPSIZE; ++i)
  {
        Value_old[i] = (int *)(ptr + MEM1 + i * TOTAL_LENGTH * sizeof(int));
        Value_new[i] = (int *)(ptr + MEM1 + (POPSIZE + i) * TOTAL_LENGTH * sizeof(int));
        for(j = 0; j < TOTAL_LENGTH; ++j)
        {
             Value_old[i][j] = 0;
             Value_new[i][j] = 0; 
        }                         
  }

  return 1;
}

[arne]

Dear members, I am new to this forum and to the C language. I have stumble to this memory allocation problem and I shave spent the last 10 hours trying to find why this piece of code does not work (I compile with Dev C++): as I try to set the vectors Value_old and Value_new to zero the code crushes. I hope you guys can help me on this. Thanks much.

AntoRoma

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

#define TOTAL_LENGTH 170
#define POPSIZE 10
#define MEM1 (2 * POPSIZE * sizeof(int *))
#define MEM2 (2 * POPSIZE * TOTAL_LENGTH * sizeof(int))
#define MEM (MEM1 + MEM2)

int main()
{
int i,j;
int **Value_old, **Value_new;
double *ptr;

ptr = malloc(MEMSIZE) ;
if(!ptr) exit(-1);

Value_old = (int **) ptr;
Value_new = (int **) (ptr + POPSIZE * sizeof(int *));
for(i = 0; i < POPSIZE; ++i)
{
Value_old[i] = (int *)(ptr + MEM1 + i * TOTAL_LENGTH * sizeof(int));
Value_new[i] = (int *)(ptr + MEM1 + (POPSIZE + i) * TOTAL_LENGTH * sizeof(int));
for(j = 0; j < TOTAL_LENGTH; ++j)
{
Value_old[i][j] = 0;
Value_new[i][j] = 0;
}
}

return 1;
}

This should not compile at all, since MEMSIZE is not defined. Please define it and see if your code works as desired.

[antoroma]

This should not compile at all, since MEMSIZE is not defined. Please define it and see if your code works as desired.

Hi:
MEMSIZE is in fact what I call MEM. But even with such change it seems that my code does not work. Any clue? Thanks much

A

[dmjpro]

if u use MEM instead of MEMSIZE then what happens with it.....

[arne]

Hi:
MEMSIZE is in fact what I call MEM. But even with such change it seems that my code does not work. Any clue? Thanks much

A

Doesn't crash when I try it. But I can't tell if it works as desired, of course :)

[antoroma]

Doesn't crash when I try it. But I can't tell if it works as desired, of course :)

Hi,
it seems that if I define ptr as a void * instead of double * the code goes thru fine. I am not sure way though.

Thanks for the help guys.

A

[arne]

Hi,
it seems that if I define ptr as a void * instead of double * the code goes thru fine. I am not sure way though.

Thanks for the help guys.

A

Yes, the return value of malloc is a pointer to void. Usually one uses it with a cast, like

char *p;
p = (char *) malloc( 100 * sizeof(char) );