Visual C++ Threads Simple Example

Question

I am trying to create a basic thread from main by passing a function to _beginthread. But My output is not getting completed.

I am getting the following output:

Starting thread
48
Main ends
I

Could someone please clarify what is wrong in the following code?

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

void test(void *param)
{
    cout << "In thread function" << endl;
    Sleep(1000); // sleep for 1 second
    cout << "Thread function ends" << endl;
    _endthread();
}


int main()
{
    cout << "Starting thread" << endl;
    cout << _beginthread(test,0,NULL);
    cout << "Main ends" << endl;
    return 0;
}

Answer 1

Because return from the main will stop any threads in your application. You need to wait untill thread will stop. Simplest solution with global var - very bad example to be honest. You need to use wait functions on thread's handle.

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

bool threadFinished = false;

void test(void *param)
{
    cout << "In thread function" << endl;
    Sleep(1000); // sleep for 1 second
    cout << "Thread function ends" << endl;
    threadFinished = true;
    _endthread();
}


int main()
{
    cout << "Starting thread" << endl;

    cout << _beginthread(test,0,NULL);
    while(!threadFinished)
    {
        Sleep(10);
    }
    cout << "Main ends" << endl;
    return 0;
}

How to use Wait functions:

HANDLE hThread;
hThread = (HANDLE)_beginthread( test, 0, NULL);
WaitForSingleObject( hThread, INFINITE );

Answer 2

You can use CreateThread method.

Simple example of multithreading.

#include <Windows.h>
#include <iostream>

using namespace std; 

DWORD WINAPI thread1(__in LPVOID lpParameter) {
    while (1) {
        std::cout << " From Thread 1 \n";
        Sleep(3000);
    }

}

DWORD WINAPI thread2(__in LPVOID lpParameter) {
    while (1) {
        std::cout << " From thread 2\n"; 
        Sleep(1000);

    }
}

int main()
{

    DWORD threadID1, threadID2; 
    HANDLE h1 = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)thread1, 0, 0,&threadID1);
    HANDLE h2 = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)thread2, 0, 0, &threadID2);

    getchar();
    return 0;
}

where thread 1 prints for every 3 secs and thread2 prints for every sec.

You can allocate stack size if your process is bigger.

StackSize explanation