15.5 保证应用程序只有一个实例运行(Mutex)

#include <iostream>
#include <Windows.h>
using namespace std;

int main()
{
    HANDLE hMutex = CreateMutex(NULL,TRUE,L"OnlyInstance");
    if (hMutex)
    {
        if (ERROR_ALREADY_EXISTS == GetLastError())
        {
            cout<<"Already exist"<<endl;
            return 0;
        }
        else
        {
            cout<<"An instance"<<endl;
        }
    }
    else
    {
        cout<<"ERROR_INVALID_HANDLE"<<endl;
    }
    system("pause");
    return 0;
}