Passing struct from array of structs to pthread_create

Question

I have created an array of structs. I am attempting to pass one element in this array to a thread through pthread_create. I am getting the following errors (they are for the 2 pthread_create calls I have in for loops):

/../a2/main.cpp|117|error: invalid conversion from ‘void (*)(serverDataStruct*)’ to ‘void* (*)(void*)’|

/../a2/main.cpp|117|error:   initializing argument 3 of ‘int pthread_create(pthread_t*, const pthread_attr_t*, void* (*)(void*), void*)’|

I have looked all over and it seems that I have the correct syntax. I will post my code below. Can someone please help me?

struct serverDataStruct
{

};

struct clientDataStruct
{

};

void serverFunc(serverDataStruct *serverData);

void clientFunc(int *ticketNum);


struct serverDataStruct serverDataArray[MAX_NUM_SERVERS];   
struct clientDataStruct clientDataArray[MAX_NUM_CLIENTS]; 

int main (  )
{
    for(int i = 0; i < numServers; i++) //create servers
    {
        pthread_create( &serverTID[i], NULL, serverFunc, (void*) &serverDataArray[i]); //PROBLEM LINE*****************************************************************

    }

    for(int i = 0; i < numCustomers; i++)
    {
        pthread_create( &clientTID[i], NULL, clientFunc, (void*) &clientDataArray[i]); //PROBLEM LINE*****************************************************************

    }
}


void *serverFunc(void *serverData)
{

}


void *clientFunc(void *clientData)
{

}

You will get a better response from the awesome SO community if you (1) narrow your code down to 10 or so lines that give the same error and (2) use the {} button to format your code neatly. — JaredC
– JaredC, Commented Feb 6, 2011 at 3:39

JaredC · Accepted Answer · 2011-02-06 04:18:27Z

1

Your functions are defined correctly, but your forward declarations are incorrect.

Change these two lines:

void serverFunc(serverDataStruct *serverData);
void clientFunc(int *ticketNum);

to match the function definitions:

void *serverFunc(void *serverData);
void *clientFunc(void *ticketNum);

Btw, please edit your question to remove all the unnecessary code :-) And format it please :-)

edited Feb 6, 2011 at 4:18

answered Feb 6, 2011 at 3:47

JaredC

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5 Comments

Robin Over a year ago

k, I've removed most of the unrelated code. and thanks, guess I needed a fresh set of eyes to see that mistake. another question, but now I am getting an error of the following format:

Robin Over a year ago

woops, continuing that previous comment: "undefined reference to `sem_open'", and I get this for all of my pthread functions (_create, _mutex, etc) and semaphore usages. Any thoughts?

JaredC Over a year ago

@Robin: What headers are you including? I would suggesting accepting this answer and opening a new question for the sem_open issue. When you post that question, try not to post more than 10 lines of code. It should be trivial to reproduce your error in 10-15 lines of code, and you might even solve your issue in the process. My suggestion would be to copy your file and keep deleting things until you have a very small amount of code that gives you the problem still.

Robin Over a year ago

will do. thanks Jared. this was my first post so just learning the proper etiquette for posting.

JaredC Over a year ago

@Robin: No need to apologize, we're here to help.

Arunmu · Accepted Answer · 2011-02-06 06:10:06Z

0

Try this:

Pthread func::

void serverFunc(void * serverData){
struct clientDataStruct * client = (struct clientDataStruct *) serverData; // just as an //example
....
}

pthread_create call:

pthread_create( &serverTID[i], NULL, serverFunc, &serverDataArray[i]);

If you are using c++ code: include this at the begining of you code after including all headers and namespaces , to prevent warnings:

extern "C"{void * serverFunc(void *);}

answered Feb 6, 2011 at 6:10

Arunmu

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