What is the difference between null and NULL in c language

The difference between null and NULL in C language is: null is a macro definition in C language. It is usually used to represent a null pointer and can be used to initialize pointer variables or determine whether the pointer is in a conditional statement. Null; NULL is a predefined constant in C language, usually used to represent a null value, used to represent a null pointer, null pointer array or null structure pointer.

#In C language, "null" and "NULL" are two different concepts.

1. null:

null is a macro definition in C language, usually used to represent a null pointer. A null pointer is a pointer that does not point to any valid memory address. In C language, null is used to represent a null pointer, which can be used to initialize pointer variables or determine whether the pointer is null in a conditional statement.

For example:

int *ptr = null;  // 将指针ptr初始化为空指针
if (ptr == null) {
 printf("指针为空\n");
}

In the above example, we use null to initialize the pointer ptr, indicating that the address it points to is empty. Then, we use a conditional statement to determine whether the pointer is null. If it is null, output "The pointer is null".

2. NULL:

NULL is a predefined constant in C language, usually used to represent a null value. Its definition may be an integer constant 0 or a pointer constant 0. In C language, NULL is usually used to represent a null pointer, null pointer array or null structure pointer.

For example:

int *ptr = NULL;  // 将指针ptr初始化为空指针
if (ptr == NULL) {
 printf("指针为空\n");
}

In the above example, we use NULL to initialize the pointer ptr, indicating that the address it points to is empty. Then, we use a conditional statement to determine whether the pointer is null. If it is null, output "The pointer is null".

Summary:

Both null and NULL are used to express the concept of empty, but in C language, they have slight differences. null is a macro definition used to represent a null pointer, and NULL is a predefined constant used to represent a null value. Their usage and meaning are similar, and they can be used to initialize pointers, determine whether pointers are null, and other operations. In actual usage, null and NULL can be used interchangeably with no obvious difference. However, in order to maintain code consistency, it is recommended to use one of them uniformly in the project to represent a null pointer or a null value.

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