1 inf.h

#pragma once


class ITest
{
public:
	virtual void sayMe() = 0;
	virtual void showMessage() = 0;
	virtual void sayBye() = 0;
};

ITest* getTestInf();

2. inf.cpp

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

class MyIMpl : public ITest
{
public:
static 	MyIMpl* instance()
	{
		if (MyIMpl::inst == nullptr)
			MyIMpl::inst = new MyIMpl;

		if (MyIMpl::inst == nullptr)
			MyIMpl::inst = new MyIMpl;

		return MyIMpl::inst;
	}

private:
	MyIMpl() : kk(1) {}
	virtual void sayMe() { cout << "I am MyImpl " << kk <<  endl; }
	virtual void showMessage() { cout << "today is a happy day" << endl; }
	virtual void sayBye() { cout << "byebye " << --kk << endl; delete this; }

private:
	static MyIMpl* inst;
	int kk;
};

MyIMpl* MyIMpl::inst = nullptr;


ITest* getTestInf()
{
	return (ITest*)(MyIMpl::instance());
}

3. infTest.cpp

// infTest01.cpp : 此文件包含 "main" 函数。程序执行将在此处开始并结束。
//

#include <iostream>
#include "inf.h"


int main()
{
    std::cout << "Hello World!\n";

    ITest* inf = getTestInf();
    inf->sayMe();
    inf->showMessage();
    inf->sayBye();
}

4. 运行结果显示