c语言指针示例_C中的空指针示例

亦凉 2023-03-05 13:24 54阅读 0赞

c语言指针示例

## 空指针 **(**NULL pointer**)** ##

The word **"NULL"** is a constant in C language and its value is **0**. In case with the pointers - if any pointer does not contain a valid memory address or any pointer is uninitialized, known as **"NULL pointer"**. We can also assign **0** (or **NULL**) to make a pointer as **"NULL pointer"**.

单词**“ NULL”**是C语言中的常量，其值为**0** 。 如果使用指针-如果任何指针不包含有效的内存地址或任何指针未初始化，则称为**“ NULL指针”** 。 我们还可以将**0** (或**NULL** )分配为**“ NULL指针”** 。

**Example:**

**例：**

In this example, there are 3 integer pointers ptr1, ptr2 and ptr3. ptr1 is initialized with the address of the integer variable num, thus ptr1 contains a valid memory address. ptr2 is uninitialized and ptr3 assigned 0. Thus, ptr2 and ptr3 are the **NULL pointers**.

在此示例中，有3个整数指针ptr1 ， ptr2和ptr3 。 ptr1用整数变量num的地址初始化，因此ptr1包含有效的内存地址。 ptr2未初始化，并且ptr3分配为0。因此， ptr2和ptr3是**NULL指针** 。

**Program:**

**程序：**

#include <stdio.h>
    
    int main(void) {
        
    	int num = 10;
    
    	int *ptr1 = &num;
    	int *ptr2;
    	int *ptr3=0;
    
    	if(ptr1 == 0)
    		printf("ptr1: NULL\n");
    	else
    		printf("ptr1: NOT NULL\n");
    
    	if(ptr2 == 0)
    		printf("ptr2: NULL\n");
    	else
    		printf("ptr2: NOT NULL\n");
    
    	if(ptr3 == 0)
    		printf("ptr3: NULL\n");
    	else
    		printf("ptr3: NOT NULL\n");
    
    	return 0;
    }

**Output**

**输出量**

ptr1: NOT NULL 
    ptr2: NULL 
    ptr3: NULL

> 翻译自: [https://www.includehelp.com/c-programs/an-example-of-null-pointer-in-c.aspx][https_www.includehelp.com_c-programs_an-example-of-null-pointer-in-c.aspx]

c语言指针示例

[https_www.includehelp.com_c-programs_an-example-of-null-pointer-in-c.aspx]: https://www.includehelp.com/c-programs/an-example-of-null-pointer-in-c.aspx