NULL 和 0， warning: assignment makes integer from pointer without a cast

[registercsdn]

大概情况是这样。
在使用pthread.h之前

#include <stdio.h>
int main(){
        int i ;
        i = NULL;
        return 0;
}

这样没有问题。

在加上pthread.h之后

#include <stdio.h>
int main(){
        int i ;
        i = NULL;
        return 0;
}

就有warning warning: assignment makes integer from pointer without a cast
如果我把NULL 改成0 就没有warning了

这是什么原因？

[hzyd_]

#ifndef NULL #define NULL 0 #ifndef NULL #define NULL (void *)0 我想第一次没warning因为NULL定义成第一个，第二次有warning因为定义成了第二个

[小笨和漂向北方]

I am not 100% sure, but I don't know that you should not assign NULL to a non-pointer variable What could happen is (my guess), somewhere in STD C, NULL is defined as #define NULL 0 but in pthread.h, NULL is defined as #define NULL (void*)0 When you include pthread.h, NULL's definition was overwritten, so you got that warning. But the root cause is: you really should not use NULL to initialize an int variable...

[小笨和漂向北方]

sorry, typo error: I am not 100% sure, but I do know that you should not assign NULL to a non-pointer variable