Thread: Having difficulty to understand pointers

Hi,

I am having difficulty to understand pointers in c language

I wrote my own code

Code:

#include<stdio.h> 

#include<stdlib.h>
         
int main ()
{  
 
 int *p = NULL;
 p = malloc (sizeof(*p));
 
 if (p == NULL)
 {
     printf("Memory is not allocated \n");
 }
 
 else 
 {
    printf("Memory is allocated \n");
    
    *p = 20;
    
    printf(" address = %p \n", p);
     
    printf(" content = %d \n", *p);
 }
 
 free(p);
        
  return 0;     
}

address = 007313A8
content = 20

1. Does it means that the pointer p points to the address 007313A8 where there are 20 stores ?

2. Is line number 8 a null pointer?

3. Is line number 27 a dangling pointer?

1- A pointer variable holds an address which points to a single memory location. malloc() alocates (reserves) a block of memory and returns the address of the first byte;

2- Yes... The NULL constant translate to (void *)0. The address "zero" is a NULL pointer (ISO 9989:9999+ §6.3.2.3-3);
You could archive the same result if you do:

Code:

p = 0;

3- You are freeing the block of memory previously allocated by malloc(). At this point, after callind free(), p will hold an address of unallocated memory, which can be treated as "invalid". But there is no memory leakage here. In this context, you can think of p as dangling...