c語言中將函數指針作為形參

Prerequisite: An Example of Null pointer in C

先決條件： C中的空指針示例

Any pointer that contains a valid memory address can be made as a NULL pointer by assigning 0.

通過分配0，可以將包含有效內存地址的任何指針設置為NULL指針 。

Example:

例：

Here, firstly ptr is initialized by the address of num, so it is not a NULL pointer, after that, we are assigning 0 to the ptr, and then it will become a NULL pointer.

在這里，首先ptr由num的地址初始化，因此它不是NULL指針，此后，我們為ptr分配0 ，然后它將成為NULL指針。

Program:

程序：

#include <stdio.h>
int main(void) {
int num = 10;
int *ptr = &num;
//we can also check with 0 instesd of NULL 
if(ptr == NULL)
printf("ptr: NULL\n");
else
printf("ptr: NOT NULL\n");
//assigning 0 
ptr = 0;
if(ptr == NULL)
printf("ptr: NULL\n");
else
printf("ptr: NOT NULL\n");
return 0;
}

Output

輸出量

ptr: NOT NULL
ptr: NULL

翻譯自: https://www.includehelp.com/c-programs/making-a-valid-pointer-as-null-pointer-in-c.aspx

c語言中將函數指針作為形參