What does null mean in c language?

In C language, null represents a null pointer, which is a predefined macro, usually defined as (void)0, used to indicate that the pointer does not point to any object or that the object has been destroyed. Therefore, unlike a void pointer, a null pointer always points to a null value and cannot be dereferenced. When comparing pointers for equality, you should use the == or != operator, and you need to check whether the pointer is null before assigning it to null. The meaning of

##null in C language

null In C language, it is a special value that represents a null pointer. It is a predefined macro, and its value is usually defined as (void *)0, where (void *) is cast to the void type pointer.

nullUse of pointers

nullPointers are used to indicate the following situations:

The pointer does not point to any object
• The object pointed to has been destroyed or is no longer valid
• The parameter of the function does not provide any value
• As the function return value, it means that the function does not return The difference between value

null pointer and void * pointer

null pointer is a void * pointer, but not vice versa. void *Pointers can point to any type of object, while nullpointers always point to null values.

Notes on using null pointers

Do not dereference the
• null pointer because it will Causes undefined behavior.
When comparing pointers for equality, use the
• == or != operator instead of < or > Operator.
Before assigning the pointer to
• null, be sure to check whether the pointer is null.

Example

The following code shows how to use the

null pointer:

<code class="c">#include <stdio.h>

int main() {
    int *ptr = NULL; // 将指针设置为 null

    if (ptr == NULL) {
        printf("指针指向空值");
    } else {
        printf("指针指向某个对象");
    }

    return 0;
}</code>

Output:

<code>指针指向空值</code>

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