Thread: Problem with realloc()

Hello,

I am using code::blocks on Windows plateform for my program. In my program, in one of the loop, I am using realloc function to increase the allocation space for one pointer to structure. It almost always fails and program does not run sucessful. For understanding, I tried the following program.

Code:

#include<stdio.h>
#include<stdlib.h>
int main(void)
{
    int i, j, loop_end=15;
    double x=10.00, *y;
    //char x='A', *y;
    y=(double*)calloc(1, sizeof(double));
    //y=(char*)calloc(1, sizeof(char));
    *y=x;
    printf("\n\n  STARTING: @ %d, value= %lf\n\n",y, *y);
    //printf("\n\n  STARTING: @ %d, value= %c\n\n",y, *y);
    for(i=0; i<=loop_end-1; i++)
    {
        printf("\n Loop No: %d\n--------------",i);
        if((realloc(y, (i+2)*sizeof(double))) == NULL)
        //if((realloc(y, (i+2)*sizeof(char))) == NULL)
        {
            printf("\n\n In loop %d mem-err occured\n",i);
            free(y);
            getchar();
            return 0;
        }
        for(j=0; j<=i; j++)
            printf("\n [%2d] Address: %d   Value: %lf",
                   j, (y+j), *(y+j));
            //printf("\n [%2d] Address: %d   Value: %c",
                   //j, (y+j), *(y+j));
         *(y+i+1)=*(y+i)+1;
    }
    printf("\n Loop completed");
    free(y);
    getchar();
    return 0;
}

When I run it for char few loops run (sometimes 5, sometimes 6) and for double it never runs sucessfully even two loops (in compilation, no warning). Please let me know where I am doing some mistake in this ??

Thanks and regards,
Amal.

realloc() doesn't always return the same pointer as input parameter.

Code:

new_pointer = realloc(old_pointer, new_size);

Thanks,
Introducing second pointer solved the problem.......

Originally Posted by amalendu

Introducing second pointer solved the problem.......

Actually, you could have used already existing pointer by assigning result of realloc() to it.

Code:

y = realloc(y, (i+2)*sizeof(double));