Difference between int *a and int **a in C

In C, the declarations int *a and int **a represent two different concepts related to pointers. Pointers play a fundamental role in memory management and data manipulation in C programming so it is important to have a clear understanding of them.

What does int * means?

This declares a pointer to an integer. It means that the variable a can store the memory address of the integer variable.

You can use another variable of type integer pointer 'a' to point to a single integer variable:

int x = 10;

int *a = &x; // 'a' points to the integer variable 'x'

a stores the address of an integer variable, so you can dereference it using the * operator to access the value of the integer it points to like *a.

Example

// C Program to illustrate 'int *' #include <stdio.h> int main() {  int x = 20;  int* a = &x;  // 'a' is a pointer to an integer  // pointing to 'x'  printf("The Value of x: %d\n", x);  printf("The Value pointed to by 'a': %d\n", *a);  return 0; } 

The Value of x: 20 The Value pointed to by 'a': 20 

In this example, int *a; declares a single-level pointer a which points to the integer variable x. a stores the memory address of the x and you can access the value of x using the *a.

Understanding 'int **'

This declares a pointer to a pointer to an integer. It means that the variable a can store the memory address of the pointer to an integer variable.

You can use a to point to a pointer to an integer:

int x = 10;

int *p = &x; // 'p' is a pointer to an integer, pointing to 'x'

int **a = &p; // 'a' is a pointer to a pointer to an integer, pointing to 'p'

In this case, a points to a pointer p that in turn points to an integer x. You can use a to access the address of p and then use *a to access the value of p which is the address of x.

Example

// C Program to illustrate 'int **' #include <stdio.h> int main() {  int x = 20;  int* p = &x;  int** a = &p;  printf("x: %d\n", x);  printf("p: %d\n", p);  printf("*p: %d\n", *p);  printf("a: %d\n", a);  printf("*a: %d\n", *a);  printf("**a: %d\n", **a);  return 0; } 

x: 20 p: -1569282476 *p: 20 a: -1569282472 *a: -1569282476 **a: 20 

In this example, int **a; declares a double-level pointer a which points to a pointer to an integer p. The p itself points to the integer variable x. You can access the value of x indirectly through a by first dereferencing a to get the address of the p and then dereferencing p to access the value of x.

Difference Between 'int *' and 'int **' in C