C++ Programs With Null

In C++, NULL is a macro used to represent a null pointer value. Null pointers are used to indicate that a pointer does not point to a valid memory address.

Syntax

pointer_variable = NULL;

Example

#include <iostream>
using namespace std;

int main() {
    int* ptr = NULL;

    if (ptr == NULL) {
        cout << "Pointer is null" << endl;
    } else {
        cout << "Pointer is not null" << endl;
    }

    return 0;
}

Output

Pointer is null

Explanation

In the above example, we first initialize a pointer variable called "ptr" to null using the NULL macro. We then use an if statement to check whether the pointer is null or not and print the appropriate message.

Use

Null pointers are useful in situations where we need to indicate that a pointer does not point to a valid memory address. For example, when we allocate memory dynamically using the "new" operator, it is possible that the allocation fails and the pointer returned is null. We can use a null pointer check to handle this situation gracefully.

#include <iostream>
using namespace std;

int main() {
    int* ptr = new int;

    if (ptr == NULL) {
        cout << "Memory allocation failed" << endl;
    } else {
        // use the allocated memory
        *ptr = 42;
        cout << "Value of pointer: " << *ptr << endl;
    }

    delete ptr;
    return 0;
}

In the above example, we allocate memory dynamically using the "new" operator. If the allocation fails, the pointer returned will be null. We can use a null pointer check to handle this situation gracefully and display an appropriate error message.

Important Points

• Null pointers are used to indicate that a pointer does not point to a valid memory address.
• The NULL macro is used to represent a null pointer value.
• It is important to use null pointer checks when working with pointers to avoid runtime errors.

Summary

In summary, null pointers play an important role in C++ programming by indicating that a pointer does not point to a valid memory address. The NULL macro is used to represent a null pointer value, and it is important to use null pointer checks when working with pointers to avoid runtime errors.