惊了 这警告和 Segmentation fault: 11 是咋回事？？？？？？？

#include <iostream> using namespace std;</iostream>

typedef struct test* t;
struct test
{
 int v;
 struct test* next;
};

int main()
{
  t a;
  a->v=1;
  a->next =nullptr;
    }

编译居然莫名其妙报了一个警告：

test.cpp:18:3: warning: variable 'a' is uninitialized when used here [-Wuniniti
alized]

a->v=1;

^

test.cpp:14:6: note: initialize the variable 'a' to silence this warning

t a;

^

= NULL

1 warning generated.

好吧 如他所愿改成

t a=NULL;

结果看的我直接迷了，Segmentation fault:11

？？？？？？？？