c语言null 值是多少,在c语言中NULL的值为0

下面是写的一段测试代码，用gdb跟踪的结果，gdb甚至可以对跟踪的变量运算后再输出：

1       #include "stdio.h"

2       int main()

3       {

4               char *a=NULL;

5

6               if (!a){

7                       printf("AA\n");

8               }

9

10

(gdb) b 4

Breakpoint 1 at 0x40052c: file main.c, line 4.

(gdb) s

The program is not being run.

(gdb) r

Starting program: /home/yjbo/temp/main

Breakpoint 1, main () at main.c:44               char *a=NULL;(gdb) n6               if (!a){(gdb) p a$1 = 0x0(gdb) p !a$2 = 1(gdb) p !a+1$3 = 2