Question

结构体作为线程函数的参数时，直接声明一个结构体的指针作为参数，和取址作为参数有什么区别？

#include "windows.h"
#include <iostream>
using namespace std;

struct THREAD_PARM_TAG
{
int a;
int b;
};
void ThreadProc(void *threadparm);

int main(int argc, char* argv[])
{
THREAD_PARM_TAG Threadparm;
Threadparm.a=1;
Threadparm.b=2;
HANDLE a = CreateThread(0,0,(LPTHREAD_START_ROUTINE)ThreadProc,&Threadparm,0,0);
MessageBox(0,0,0,0);
return 0;
}

void ThreadProc(void *threadparm)
{
cout<<((THREAD_PARM_TAG *)threadparm)->a;
}
如果将main函数改为：
int main(int argc, char* argv[])
{

THREAD_PARM_TAG *Threadparm;
Threadparm->a=1;
Threadparm->b=2;
HANDLE a = CreateThread(0,0,(LPTHREAD_START_ROUTINE)ThreadProc,Threadparm,0,0);
MessageBox(0,0,0,0);
return 0;
}
之后为什么就不能取到a=1的值呢？

Answer 1

第二种写法 Threadparm 是野指针，声明了指针却没有明确地指向确定的地址，这样访问程序可能会崩溃的。
大概应该是这样写：

THREAD_PARM_TAG Threadparm;

THREAD_PARM_TAG *pThreadparm = &Threadparm;

pThreadparm->a=1;
pThreadparm->b=2;
HANDLE a = CreateThread(0,0,(LPTHREAD_START_ROUTINE)ThreadProc,pThreadparm,0,0);