I am getting a segmentation fault failure in my code. I have narrowed down the code to this simplified version. I have removed the obvious malloc checks as there was no failure in malloc . I am getting an error when I try to access a[0] in do_something but when I try to access the same in the give_mem_and_do it doesnt fail. I am not able to comprehend the reason . I am passing the address of a location that is already allocated on the heap. So why should it in fail in accessing this location.
#include <stdio.h>
#include <stdlib.h>
struct abc
{
int *a;
int b;
};
typedef struct abc thing;
int do_something( thing ** xyz, int a)
{
printf ("Entering do something \n");
(*xyz)->a[0] = a;
return 0;
}
int give_mem_and_do (thing ** xyz, int *a)
{
int rc;
printf ("\n Entered function give_mem_and_do \n");
if (*xyz == NULL)
{
*xyz = (thing *)malloc ( sizeof (thing) );
(*xyz)->a = (int *) malloc (sizeof (int)*100);
}
printf (" Calling do_something \n");
rc = do_something (xyz, *a);
return 0;
}
int main ()
{
thing * xyz;
int abc = 1000;
give_mem_and_do (&xyz,&abc);
#include <stdio.h>
#include <stdlib.h>
struct abc
{
int *a;
int b;
};
typedef struct abc thing;
int do_something( thing ** xyz, int a)
{
printf ("Entering do something \n");
(*xyz)->a[0] = a;
return 0;
}
int give_mem_and_do (thing ** xyz, int *a)
{
int rc;
printf ("\n Entered function give_mem_and_do \n");
if (*xyz == NULL)
{
*xyz = (thing *)malloc ( sizeof (thing) );
(*xyz)->a = (int *) malloc (sizeof (int)*100);
}
printf (" Calling do_something \n");
rc = do_something (xyz, *a);
return 0;
}
int main ()
{
thing * xyz;
int abc = 1000;
give_mem_and_do (&xyz,&abc);
return 0;
}
Following is the output of this code
Entered function give_mem_and_do
Calling do_something
Entering do something
Segmentation fault (core dumped)
