C++回调实现

实际应用场景：

一个线程类读取实时股票信息，在读取完成后，调用回调函数，把读取到的结果返回上级类。

下面的是一个回调示例,两个数相加,在一个线程内运算结果后,通过回调回传计算结果

CBTest.h

//CBTest.h
//本示例演示了回调函数实现,在入口程序设置相关参数和回调函数后
//用一个线程进行运算,得到结果后通过回调函数,回传运算结果

#pragma once

#include <Windows.h>

class CBTest
{
	//声明回调函数,
	//sum运算结果回传, p目标类指针
	typedef void(CALLBACK *CBFunc)(int sum, void* p);
	typedef CBFunc CBHandler;

public:
	CBTest();
	virtual ~CBTest();

	//运算,并设置回调相关信息
	void Op(int a, int b, CBFunc handler, void* p);

	//检测是否正在运作
	bool IsRuning();

private:

	//void SetRunning(bool running);

	//进行运算的线程
	static DWORD CALLBACK ThreadOp(LPVOID p);

	void Calculate();
private:

	bool mNeedOp;
	int a;
	int b;
	HANDLE mThreadOp;
	HANDLE mMutex;

	//缓存回调函数指针
	CBHandler mCBHandler;
	void* mCBObj;
};

 CBTest.cpp

//CBTest.cpp

#include "CBTest.h"

CBTest::CBTest()
{
	mNeedOp = false;
	a = 0;
	b = 0;
	mThreadOp = INVALID_HANDLE_VALUE;
	mMutex = CreateMutexA(NULL, false, "CBTestMutex");

	mCBHandler = NULL;
	mCBObj = NULL;

	//创建线程
	LPDWORD p = NULL;
	mThreadOp = CreateThread(NULL, 0, ThreadOp, this, 0, p);
}

CBTest::~CBTest()
{
	if (mThreadOp != INVALID_HANDLE_VALUE)
	{
		CloseHandle(mThreadOp);
		mThreadOp = INVALID_HANDLE_VALUE;
	}

	mCBHandler = NULL;
	mCBObj = NULL;
}

void CBTest::Op(int a, int b, CBFunc handler, void* p)
{
	WaitForSingleObject(mMutex, INFINITE);
	this->a = a;
	this->b = b;

	//缓存回调函数
	mCBHandler = handler;
	mCBObj = p;

	mNeedOp = true;
	ReleaseMutex(mMutex);
}

bool CBTest::IsRuning()
{
	bool op = false;
	//Mutex演示
	WaitForSingleObject(mMutex, INFINITE);
	op = mNeedOp;
	ReleaseMutex(mMutex);
	return op;
}
//
//void CBTest::SetRunning(bool running)
//{
//	WaitForSingleObject(mMutex, INFINITE);
//	mNeedOp = running;
//	ReleaseMutex(mMutex);
//}

DWORD CALLBACK CBTest::ThreadOp(LPVOID p)
{
	CBTest* test = (CBTest*)p;
	while (true)
	{
		test->Calculate();
	}
}

void CBTest::Calculate()
{
	if (!IsRuning())
	{
		Sleep(5);
		return;
	}
	
	//故意做的一个延时
	Sleep(1000);

	int sum = a + b;
	if (mCBHandler != NULL)
	{
		(*mCBHandler)(sum, mCBObj);
	}
	WaitForSingleObject(mMutex, INFINITE);
	mNeedOp = false;
	ReleaseMutex(mMutex);
}

Main.cpp

//Main.cpp
#include <cstdio>
#include <windows.h>
#include <string>

#include "CBTest.h"

//////////////////////////////////////////////////////////////////////////

//多个参数拼合成一个std::string
std::string format(const char *format, ...)
{
	char ret[512] = { 0 };
	va_list argptr;
	va_start(argptr, format);
	vsprintf_s(ret, format, argptr);
	va_end(argptr);
	return ret;
}

//Log显示函数,显示有输出时间
void LogShow(const char* str, ...)
{
	if (str == NULL || strlen(str) == 0)
	{
		return;
	}
	SYSTEMTIME sys;
	GetLocalTime(&sys);


	char ret[512] = { 0 };
	va_list argptr;
	va_start(argptr, str);
	vsprintf_s(ret, str, argptr);
	va_end(argptr);


	int strLen = strlen(ret);
	char change[256] = { 0 };
	char retText[256] = { 0 };
	int index = 0;
	while (index < strLen && index < 256)
	{
		if (ret[index] == '\n')
		{
			change[index] = '\n';
		}
		else
		{
			if (strLen - index>0)
			{
				strcpy_s(retText, ret + index);
			}
			break;
		}
		index++;
	}

	std::string retStr;
	if (strlen(change) > 0)
	{
		retStr = format("%s%d/%d/%d %02d:%02d:%02d:%03d %s\n", change, sys.wYear, sys.wMonth, sys.wDay, sys.wHour, sys.wMinute, sys.wSecond, sys.wMilliseconds, retText);
	}
	else
	{
		retStr = format("%d/%d/%d %02d:%02d:%02d:%03d %s\n", sys.wYear, sys.wMonth, sys.wDay, sys.wHour, sys.wMinute, sys.wSecond, sys.wMilliseconds, ret);
	}

	printf(retStr.c_str());
}

//////////////////////////////////////////////////////////////////////////

//回调函数为一个单独的函数
static void CALLBACK ShowResult(int sum, void* p)
{
	LogShow("结果是:%i\n", sum);
}

//类中回调测试
class Test
{
public:

	void Cal(int a, int b)
	{
		mCBTest.Op(a, b, &Test::cb, this);
	}

	bool IsRunning()
	{
		return mCBTest.IsRuning();
	}
private:
	static void CALLBACK cb(int sum, void* self)
	{
		Test* test = (Test*)self;
		test->Show(sum);
	}

	void Show(int sum)
	{
		LogShow("Test结果是:%i\n", sum);
	}
private:

	CBTest mCBTest;
};

void main()
{
	//注:test与下面的t会分别创建运算线程,
	CBTest test;
	//单独函数的回调
	test.Op(3, 4, &ShowResult, NULL);

	Test t;

	while (t.IsRunning())
	{
		Sleep(10);
	}
	//类中函数的回调
	t.Cal(10, 12);

	for (int i = 0; i < 100; i++)
	{
		while (t.IsRunning())
		{
			Sleep(20);
		}
		int a = i;
		int b = 0;

		t.Cal(a, b);
	}

	char c = 0;
	scanf_s("%i", c);
}