CODEWITHSUNDEEP
c++multithreadingfunctionparametersg++
xcdemon05
xcdemon05

Reputation: 1432

Passing functions as parameters in order to simplify thread creation

I'm trying to write a small piece of code that just makes using CreateThread() slightly more clean looking. I can't say that I'm really intending on using it, but I thought it would be a fun, small project for a newer programmer like myself. Here is what I have so far:

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

void _noarg_thread_create( void(*f)() )
{
    cout << "Thread created...\n" << endl;
    Sleep(10);
    CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)f, NULL, 0, NULL);
}

template <typename T>
void _arg_thread_create( void(*f)(T), T* parameter)
{
    cout << "Thread created...\n" << endl;
    Sleep(10);  
    CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)*f, parameter, 0, NULL); 
}


void printnums(int x)
{
    for(int i = x; i < 100; i++)
    {
        cout << i << endl;
    }
}

void printnumsnoarg()
{
    for(int i = 0; i < 100; i++)
    {
        cout << i << endl;
    }
}


int main()
{
    cin.get();
    _noarg_thread_create( &printnumsnoarg );
    cin.get();
    int x = 14;
    _arg_thread_create( &printnums, &x );
    cin.get();
}

Basically I have two functions that will call two different presets for CreateThread: one for when a parameter is needed in the thread, and one for when no parameter is needed in the thread. I can compile this with the g++ compiler (cygwin), and it runs without any errors. The first thread gets created properly and it prints out the numbers 0-99 as expected. However, the second thread does not print out any numbers (with this code, it should print 14-99). My output looks like this:

<start of output> 

$ ./a.exe

Thread created...

0     
1
2   
3
.
.
.        
97
98   
99


Thread Created...



<end of output>

Any ideas why the second thread isn't working right?

Upvotes: 1

Views: 131

Answers (1)

mikyra
mikyra

Reputation: 10377

you actually seem to miss you're passing a pointer to your printnums(int x) function. As the storage location of x in your main function will be a lot bigger than 100 your loop never runs.

You should try to change printnums to:

void printnums(int *x)
{
    for(int i = *x; i < 100; i++)
    {
        cout << i << endl;
    }
}

I guess everything will work as expected then.

Upvotes: 1

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