The difference between null and 0 in C language

In C language, the difference between NULL and 0 is as follows: NULL is a null pointer constant, and 0 is an integer constant; the data type of NULL is void *, and the data type of 0 depends on the context; NULL and 0 cannot be directly compared for equality, and the type of 0 needs to be explicitly converted; NULL is used to represent a null pointer, and 0 is used to represent various values, such as zero value or null pointer; in old code, 0 may be used as a null pointer, but for For safety, it is recommended to use NULL to initialize pointer variables. 0 can only be used for integer variables.

The difference between NULL and 0 in C language

In C language,NULL Although 0 are constants, they represent different concepts:

1. Value and type

• NULL is a special pointer constant, which represents a null pointer pointing to a non-existent memory address.
• 0 is an integer constant whose value is equal to zero.

2. The data type of data type

• NULL is void *, which is Pointer to type void. The data type of
• 0 depends on its context, it can be an integer or float such as int, long, float Point type.

3. Compare

• NULL and 0 cannot be directly compared for equality, because their Different types.
• Requires explicit conversion of 0 to void * type for comparison: NULL == (void *)0

4. Purpose

• #NULL is usually used to initialize pointers, indicating that they do not point to any valid memory address.

• 0 is used to represent various values, such as:

  • Integer constant: represents a zero value.
  • Pointer constant: represents a null pointer (not recommended).
  • Boolean values: 0 means false, non-zero means true (although there is no explicit boolean type in C).

5. Notes

• Before C99, NULL was defined as 0. Therefore, in old code, 0 may be used as a null pointer constant.
• For pointer variables, it is safer to initialize with NULL because it clearly indicates that the pointer points to an invalid address, whereas 0 may be mistaken for a valid address.
• For integer variables, 0 is a valid zero value, while NULL can only be used for pointers.

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