pointer arithmetic

[xyz4rm]

Hi, here is a structure with 2 pointer to integer

I want increment the value of x by 1, (tt.c) ++ is not increment to 11 rather it increments to 14. how do i increment the value pointed by tt.c ? any help?
thx

#include <stdio.h>

main () {typedef struct {

int *c;        int *d; }ABC; ABC  tt;

int x=10, y=11;    tt.c = &x;      tt.d = &y;

(tt.c)++ ;  // lincrementing = 10+1

printf ("value of x %u\n", (tt.c)) ;  }

[clu82]

To increment THE VALUE STORED in x: (*tt.c)++

Also, this

printf("value of x %u/n", (tt.c))

isn't displaying the value stored in x. It's displaying the address of x. You need to dereference it.

clu82

[Dave Evans]

Here's a suggestion: when you don't understand program output, sprinkle a few printf()s around.

consider:

#include <stdio.h>

main () 
{
  typedef struct {
        int *c;
        int *d; 
  }ABC; 

  ABC  tt;

  int x=10, y=11;    
  tt.c = &x;      
  tt.d = &y;

  printf("tt.c = %p\n", tt.c);
  printf("*tt.c = %d\n", *tt.c);
  printf("tt.d = %p\n", tt.d);
  printf("*tt.d = %p\n", *tt.d);

  // the following makes tt.c point to who-knows-where
  (tt.c)++ ;  // lincrementing = 10+1
  printf("After incrementing tt.c = %p\n", tt.c);
  printf("After incrementing tt.c, *tt.c = %d\n", *tt.c);

  // tt.c is a pointer; you are printing the value of the pointer,
  // not the value of who-knows-what that tt.c is pointing to
  printf ("value of x %u\n", (tt.c)) ;  
  printf ("value of x %p\n", (tt.c)) ;  
  return 0;
}

Dave

[WaltP]

The reason (tt.c)++ incremented by 4 is because the value is a pointer and pointers are 4 bytes, to keep them aligned the language will increment by it's size.

Two other points:

First, you need code tags around the entire program, not each line

Second, your formatting is abysmal (based on the removal of code tags). It should be more like:

#include <stdio.h>
int main () 
{
    typedef struct 
    {
        int *c;
        int *d; 
    }ABC; 
    ABC  tt;
    int x=10, y=11;
    
    tt.c = &x;
    tt.d = &y; 
    (tt.c)++ ;  // lincrementing = 10+1 
    printf ("value of x %u\n", (tt.c)) ;
    return 0;
}