Pointers

Pointers represent the address of a location in memory, serving as the connections that hold the pieces of linked structures together. A variable storing a pointer to a given data item can provide more freedom than storing a copy of the item itself.

Analogy: A cell-phone number can be thought of as a pointer to its owner as they move about the planet.

Syntax

In C/C++ syntax:

• A pointer p is assumed to give the address in memory where a particular chunk of data is located.
• We use *p to denote the item that is pointed to by pointer p – de-reference.
• We use &x to denote the address of (i.e. pointer to) a particular variable x.
• A special NULL pointer value is used to denote structure-terminating or unassigned pointers.

Example

int myAge = 23; // An int variable
int* ptr = &myAge; // A pointer variable, with the name ptr, that stores the address of myAge  
 
// Output the value of myAge (23)  
printf("%d\n", myAge);  
 
// Output the memory address of myAge (0x00220022)  
printf("%p\n", &myAge);  
 
// Output the memory address of myAge using the pointer (0x00220022)  
printf("%p\n", ptr);  
 
// Dereference: Output the value of myAge using the pointer (23)  
printf("%d\n", *ptr);

Structs

The -> operator in C is specifically used for accessing members of a struct through a pointer. When we have a pointer to a struct, we use the -> operator to access the fields of the struct that the pointer points to.

struct example { 
	int a; 
};
 
struct example e;
e.a = 5;
 
struct example *p = &e; 
 
// Returns 5
printf(p->a); // This would return 5, and is equivalent to (*p).a or e.a