下面的C代碼片段:空指針作爲參數
[...]
void f1(void* a){
printf("f(a) address = %p \n",a);
a = (void*)(int*)malloc(sizeof(int));
printf("a address = %p \n",a);
*(int*)a = 3;
printf("data = %d\n",*(int*)a);
}
void f(void){
void* a1=NULL;
printf("a1 address = %p \n",a1);
f1(a1);
printf("a1 address = %p \n",a1);
printf("Data.a1 = %d\n",*(int*)a1);
}
[...]
結果
a1 address = (nil)
f(a) address = (nil)
a address = 0xb3f010
data = 3
a1 address = (nil)
Segmentation fault (core dumped)
爲什麼不a1
保持已分配給它的函數地址?
查找「按價值傳遞」。 – Mysticial
因爲你通過它傳遞價值。 –
http://c-faq.com/ptrs/passptrinit.html –