[英]Function pointers in C++
I used CreateThread function to write a class like C# BackgroundWorker in C++.My code: 我使用CreateThread函数在C ++中编写类似C#BackgroundWorker的类。我的代码:
BackgroundWorker.h: BackgroundWorker.h:
class BackgroundWorker
{
private :
HANDLE _threadHandle;
unsigned int _threadCallcounter;
DWORD _threadID;
public:
BackgroundWorker();
~BackgroundWorker();
virtual DWORD WINAPI Function(LPVOID vpPram);
}
BackgroundWorker.cpp: BackgroundWorker.cpp:
#include "BackgroundWorker.h"
void BackgroundWorker::DoWork()
{
this->_threadHandle = CreateThread(NULL,
0,this->Function,&this->_threadCallcounter,
0, &this->_threadID); // !!!***This part throws an error***!!!
}
Then I created another class that derived from BackgroundWorker: 然后我创建了另一个派生自BackgroundWorker的类:
ListenThread.cpp: ListenThread.cpp:
class ListenThread :public BackgroundWorker
{
DWORD WINAPI Function(LPVOID vpPram)
{
//DO somthing...
return 0;
}
};
But that line gives me the following error: 但该行给了我以下错误:
non - standard syntax;
非标准语法; use '&' to create a pointer to member
使用'&'创建指向成员的指针
The function pointer that CreateThread expects must have this signature: CreateThread期望的函数指针必须具有以下签名:
DWORD WINAPI ThreadProc(LPVOID lpParameter);
When you create a member function it gets an invisible "this" parameter as first argument, so you declare something like this implicitly: 当你创建一个成员函数时,它会获得一个不可见的“this”参数作为第一个参数,所以你隐式地声明这样的东西:
DWORD WINAPI ThreadProc(BackgroundWorker *this, LPVOID lpParameter);
Create a static member function to omit the this pointer and if you need that pointer inside the thread routine pass it as the void * parameter 创建一个静态成员函数来省略this指针,如果需要在线程例程中使用该指针,则将其作为void *参数传递
Your error message means you need to pass pointer to function as &Function
, not Function
in DoWork
. 您的错误消息意味着您需要将指针传递给函数作为
&Function
,而不是Function
在DoWork
。
Unfortunately fixing this won't help. 不幸的是修复这个没有用。
CreateThread
doesn't work with (non-static) member functions. CreateThread
不适用于(非静态)成员函数。 A solution is to create a static method to use as the actual thread start function. 解决方案是创建一个静态方法以用作实际的线程启动函数。
Check this example: 检查此示例:
#include <Windows.h>
#include <iostream>
class BackgroundWorker
{
private :
HANDLE _threadHandle;
DWORD _threadID;
public:
static DWORD WINAPI StaticThreadStart(void * Param) {
BackgroundWorker * This = static_cast<BackgroundWorker *>(Param);
return This->Function();
}
virtual DWORD Function() {
return 0;
}
void DoWork() {
_threadHandle = CreateThread(NULL, 0, StaticThreadStart, this, 0, &_threadID);
}
};
class ListenThread : public BackgroundWorker {
DWORD Function() override {
std::cout << "Working...\n";
return 0;
}
};
int main()
{
ListenThread cl;
cl.DoWork();
// Call pause to wait for new thread in this example
system("pause");
return 0;
}
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