Pointers in C

**lio** · 12-10-2010

I have problems with pointers wich I am trying to clear .Are my comments correct

Code:

 #include <stdio.h>

int main()
{   
  int * one=NULL;
  printf("%d\n",one);
  int a=5;
  one=&a;
  printf("%p\n",one);//printing the the value in pointer one
  printf("%p\n",&a); 
  printf("%d\n",*one); //printing the value where the value(address) of the pointer is pointing 
  printf("%p\n",&one);
   if (one)
   printf("GOOD\n");
   getch();
   return 0;
}

**cnewbie1** · 12-10-2010

What are you trying to do and what's the problem? It looks like you create an int variable, then an int pointer to that variable, and then you print out the variable and the pointer (not in that order).

**hellork** · 12-10-2010

Pointers are variables.
Cprogramming.com FAQ > A tutorial on pointers

Also getch(); is not defined in stdio.h and on Linux getch() only works within special curses applications that disable line buffering. For something more portable:
Cprogramming.com FAQ > Stop my Windows Console from disappearing everytime I run my program?
Cprogramming.com FAQ > How do I get my program to wait for a keypress?

Or this little gem, which is evil outside of keeping a local console open because it does not check for EOF:
while (getchar()!='\n');

**anduril462** · 12-10-2010

Your comments sound correct. A pointer is just a variable that stores an address. To clarify, here is what each printf is doing:

Code:

  printf("%d\n",one);

The value in one is an address, not an integer, so this isn't correct. You properly print the value pointed to by one in your 4th printf.

Code:

  printf("%p\n",one);//printing the the value in pointer one

one contains an address, so you are printing the address contained in one (which you initialized to NULL, so it will likely print 0x000000)

Code:

  printf("%p\n",&a);

a is an integer, so you are printing the address of the variable a

Code:

  printf("%d\n",*one); //printing the value where the value(address) of the pointer is pointing

You are printing the value contained at the address stored in one. Since you initialized one to NULL, this will probably seg fault (can't read from NULL).

Code:

  printf("%p\n",&one);

You are printing the address of the variable one (this should be close to &a since they are adjacent on the stack).

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