In C language, the NULL macro is used to represent a null pointer, which is a pointer that does not point to any valid memory location. The NULL macro is defined in the <stdio.h> and <stddef.h> headers and is usually set to 0.

Here is an example of a null pointer:

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#include <stdio.h> int main() {    int* p = NULL;  // p is a null pointer    printf("%p\n", p);  // prints 0    return 0; }

In this example, the pointer p is initialized with the value NULL, meaning it does not point to any valid memory location. Attempting to dereference a null pointer will result in undefined behavior, so it's important to check if a pointer is null before dereferencing it.

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#include <stdio.h> int main() {    int* p = NULL;  // p is a null pointer    if (p != NULL) {        printf("%d\n", *p);    } else {        printf("p is a null pointer\n");    }    return 0; }

The NULL macro can also be used to initialize a variable of any pointer type to a null pointer.

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#include <stdio.h> int main() {    int* p1 = NULL;    char* p2 = NULL;    double* p3 = NULL;    return 0; }

It's also worth noting that, the NULL pointer is not the same as an uninitialized pointer, an uninitialized pointer has an indeterminate value and it could be any value