How to pass multiple parameters to a thread function

Question

I have created a function for a thread, but I want to pass multiple parameters to the function.

Here's my source code :

#include "work.h"
#include <stdio.h>
#include <unistd.h>
#include <pthread.h>    // compile with -lpthread

int count = 20;

void* ChildProc(void* arg)
{
    int i;

    for(i = 1; i <= count; i++)
    {   
        printf("%s:%d from thread <%x>\n", arg, i, pthread_self());
        DoWork(i);
    }

    return NULL;
}

void ParentProc(void)
{
    int i;

    for(i = count / 2; i > 0; i--)
    {
        printf("Parent:%d from thread <%x>\n", i, pthread_self());
        DoWork(i);
    }
}

int main(void)
{
    pthread_t child;

    pthread_create(&child, NULL, ChildProc, "Child");

    ParentProc();

    pthread_join(child, NULL); // make child a non-daemon(foreground) thread
}

Now how do I pass multiple parameter to ChildProc() method?

One way is either pass an array or a structure. But what if I want to pass multiple variables without an array or a structure?

Is there any other method similar to pthread_create() which can support multiple parameters? — Searock, Sep 09 '10 at 05:59

mmonem · Answer 1 · 2010-09-09T06:08:47.157

7

A fast and junk answer is to create a struct to hold all parameter and pass its pointer

edited Sep 09 '10 at 06:08

answered Sep 09 '10 at 05:55

mmonem

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How do I create parameter class object in C? – Searock Sep 09 '10 at 05:56
Forget **class object**. in C: Create a struct to hold parameters, instantiate a variable from it, set the parameters, pass the pointer of this variable over – mmonem Sep 09 '10 at 06:07
7

There's nothing junk about the fast answer - it is the correct answer. – Jonathan Leffler Sep 09 '10 at 06:09

Johann Gerell · Answer 2 · 2010-09-09T10:39:52.923

3

One way is either pass a array or a structure.

That's the way. Pointer to a structure, that is.

what if I want to pass multiple variables withous a array or a structure?

Then you're out of luck. Array or a pointer to a structure is what you need.

edited Sep 09 '10 at 10:39

answered Sep 09 '10 at 05:57

Johann Gerell

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Is there any other method similar to pthread_create() which can support multiple parameters? – Searock Sep 09 '10 at 05:59
3

@Searock: no - there isn't any other method similar to pthread_create() which supports multiple parameters. – Jonathan Leffler Sep 09 '10 at 06:08

score 1 · Accepted Answer · edited Sep 09 '10 at 07:15

1

You can pass a void * buffer stream and if you know the lengths then you can access them. Its similar to implementation of GArrays.

How do you create them?

void *buffer = malloc(sizeofelements);
memcpy(buffer,element1,sizeof element1);
memcpy(buffer+sizeof element1,element2, sizeof element2);

NOTE: The above is not a compilable C code. You need to work on it.

You can use something of the above sort.

You can later access the variables as you already know the size

edited Sep 09 '10 at 07:15

RBerteig

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answered Sep 09 '10 at 06:15

Praveen S

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I meant it wont compile if you CTRL-C CTRL-V, However if you use the code and the function calls correctly it will work. Like`memcpy(dest,ptr,size);` and what i have written is enough to understand one has to do as stated here. – Praveen S Sep 09 '10 at 10:33
1

-1 This is exactly the same way as passing a pointer to a struct except that it's not as type safe and is not as readable. – JeremyP Sep 10 '10 at 15:50
@JeremyP - You forgot to add without actually declaring the structure in your comment. I agree with your other points but the OP asked for an alternative. – Praveen S Sep 11 '10 at 06:35
@Praveen S: My point is that this isn't really an alternative. It's doing exactly the same thing as passing a struct but without explicitly defining the structure of the block of memory. – JeremyP Sep 12 '10 at 16:37

How to pass multiple parameters to a thread function

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