为什么在以下代码中出现分段错误？

Question

Nothing gets printed in my code. No compiler issue. Why doesn't it print anything? I get no warning either.

    #include <stdio.h>
    #include <string.h>

    int main() 
    { 
        struct site 
        { 
            int no_of_pages;
            char name[20];
        }; 
        struct site *ptr;
        ptr->no_of_pages = 665;
        printf("%d\n",ptr->no_of_pages); 

        char array[20];
        strcpy(array, "hello");
        strcpy(ptr->name, "Singularity");
        printf("%s\n",ptr->name);   
        return 0; 
}

Answer 1

Yes, there is a warning which points out the root of your problem:

$ cc -Wall test.c 
test.c:13:5: warning: variable 'ptr' is uninitialized when used here
      [-Wuninitialized]
    ptr->no_of_pages = 665;
    ^~~

Answer 2

首先初始化指针

struct site *ptr = malloc(sizeof(struct site));