CODEWITHSUNDEEP
cmultithreadingwinapi
Tommy
Tommy

Reputation: 176

How to create a very basic thread function in C

I have a limited amount of c experience and virtually no experience using threads. If there is a simple way to wrap the "forever" function into a thread and allow main() to continue running, please let me know how it can be done. This example is totally impractical of course but if I can get it to work, I think its a good starting point. Maybe its not even possible? But would like to know. Thanks!

//
#include <Windows.h>
#include <stdlib.h> 
#include <iostream>
#include <stdio.h>
#include "stdafx.h"

void foreverFunction(); // function prototype

int myNumber=1;

void main()
{

    foreverFunction();   // call forever (looping function), would like get it running as a separate thread so that the code below can continue.
    while (myNumber != 0 ){
        printf("Enter a number (0 to exit): ");
        scanf("%d",&myNumber);
        printf("Entered: %d\n",myNumber);
    }

}


// function below should report the current value of myNumber every second
void foreverFunction(){
while (myNumber>0){
    printf ("\nThis will run until the user enters 0, Last value entered was %d\n",myNumber);
    Sleep(1000);
    }
}

Upvotes: 0

Views: 120

Answers (3)

Tommy
Tommy

Reputation: 176

Here is my updated code (from the example above) which is working and doing exactly what I expect. Thanks to all. 

#include <windows.h>
#include <WinBase.h>
#include <stdlib.h> 
#include <iostream>
#include <stdio.h>
#include "stdafx.h"
#include <process.h>

int myNumber=1;

// function below should report the current value of myNumber every second
unsigned __stdcall foreverFunction(void* pArguments){

printf("The thread is started...\n");

while (myNumber>0){
    printf ("Selected number: %d\n",myNumber);
    Sleep(1000);
    }
printf("The thread as exited... \n");
return NULL;
}      

void main()
{
    HANDLE hThread;
    unsigned threadID;

    hThread = (HANDLE)_beginthreadex( NULL, 0, &foreverFunction, NULL, 0, &threadID );

    while (myNumber != 0 ){
        printf("Enter a number (0 to exit): ");
        scanf("%d",&myNumber);
        printf("Entered: %d\n",myNumber);
    }

}

The Console Output:

Enter a number (0 to exit): The thread is started...
Selected number: 1
Selected number: 1
Selected number: 1
Selected number: 1
Selected number: 1
3
Entered: 3
Enter a number (0 to exit): Selected number: 3
Selected number: 3
Selected number: 3
Selected number: 3
Selected number: 3
Selected number: 3
Selected number: 3
54
Entered: 54
Enter a number (0 to exit): Selected number: 54
Selected number: 54
Selected number: 54
Selected number: 54

Upvotes: 0

robin.koch
robin.koch

Reputation: 1223

for a simple program like yours you can use beginthread()

_beginthread(foreverfunction, 0, NULL);

the first argument is a function pointer (the name of your function). The second is the stack size and can be 0. The third is a parameter you want give your function (more specific, a pointer to the parameter). If you have multiple arguments you have to pack them into a struct

another function you could use in Windows is CreateThread() for Linux (POSIX) see haris answer

Upvotes: 1

Haris
Haris

Reputation: 12272

Edited

If you're working on linux, you can use the pthread for this purpose. For your example, to keep the function running forever, you can do something like

pthread_t thread1;

pthread_create (&thread1, NULL, (void *) &foreverFunction);
pthread_join(thread1, NULL);

Now, your function won't exit until main exits. This is taken care by the pthread_join() call.

Upvotes: 0

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