passing arg 3 of `pthread_create' from incompatible pointer type

wallwaters · 05-27-2005, 11:01 AM

passing arg 3 of `pthread_create' from incompatible pointer type

I do not understand this warning.

Following is my code . what is that warning. I dont see any thing wrong in code. Please help me.

Result vSend(int rxLength);
void *sendThread(void *rxLength);

void main()
{
vSend(100);
}
Result vSend(int rxLength)
{
Result status = PENDING;
pthread_t sendThread;
int tRetVal;
App_Report("vSend %d",rxLength);
tRetVal = pthread_create( &sendThread, NULL, &sendThread, &rxLength);
return status;
}

void *sendThread(void *rxLength)
{
int *length = (int *) rxLength;
print("Length %d"length );
return NULL;
}

passing arg 3 of `pthread_create' from incompatible pointer type

Thanks
Suneel

freegianghu · 05-27-2005, 11:47 AM

Quote:

Originally posted by wallwaters
passing arg 3 of `pthread_create' from incompatible pointer type

I do not understand this warning.

Following is my code . what is that warning. I dont see any thing wrong in code. Please help me.

Result vSend(int rxLength);
void *sendThread(void *rxLength); // change to void sendThread(void *rxLength);

void main()
{
vSend(100);
}
Result vSend(int rxLength)
{
Result status = PENDING;
pthread_t sendThread;
int tRetVal;
App_Report("vSend %d",rxLength);
tRetVal = pthread_create( &sendThread, NULL, &sendThread, &rxLength);
return status;
}

void *sendThread(void *rxLength) // change to void sendThread(void *rxLength);
{
int *length = (int *) rxLength;
print("Length %d"length );
return NULL;
}

passing arg 3 of `pthread_create' from incompatible pointer type

Thanks
Suneel

rjlee · 06-02-2005, 03:23 PM

freegianghu, you can't return NULL; from a function with a void return-type.

The problem is that sendThread is defined both as a function (by a forward declaration) and as a variable. The variable masks the definition of the function, and so both sendThread arguments passed to pthread_create are of type pthread_t.

Since the third argument to pthread_create is supposed to be a callback function, not a pthread_t, this won't compile.

freegianghu · 06-02-2005, 08:58 PM

Quote:

Originally posted by rjlee
freegianghu, you can't return NULL; from a function with a void return-type.

The problem is that sendThread is defined both as a function (by a forward declaration) and as a variable. The variable masks the definition of the function, and so both sendThread arguments passed to pthread_create are of type pthread_t.

Since the third argument to pthread_create is supposed to be a callback function, not a pthread_t, this won't compile.

Sorry, I made a mistake

. Its should be void *sendThread(void *rxLength)

Have a nice day,
Giang Hu

gozlemci · 03-06-2010, 06:24 PM

Hi there;
I've encountered with the same problem in my code with some extra problems.Here are the code :

Code:

/*
 * pmutex.c
 *
 *  Created on: Mar 7, 2010
 */

#include <pthread.h>
#include <stdio.h>

pthread_mutex_t cntr_mutex = PTHREAD_MUTEX_INITIALIZER;

long protVariable = 0L;

void myThread(void *arg)
{

	int i,ret;

	for(i=0 ; i<10000 ; i++)
	{

		ret = pthread_mutex_lock(&cntr_mutex);

		if(ret == 0)
		{
			protVariable++;
		}


		ret = pthread_mutex_unlock(&cntr_mutex);

		if(ret == 0)
		{
			printf("ret is zero.\n");
		}

	}

	pthread_exit(NULL);
}

#define MAX_THREADS 10

int main()
{

	int ret,i;
	pthread_t threadIds[MAX_THREADS];

	for( i=0 ; i<MAX_THREADS ; i++)
	{

		//below code gives error: passing argument 3 of ‘pthread_create’ from incompatible pointer type
		//and undefined reference to `pthread_create'
		ret = pthread_create(&threadIds[i] , NULL , myThread , NULL);
		if(ret != 0)
		{

			printf("error creating thread %d\n",(int)threadIds[i]);
		}

		//below code gives error: undefined reference to `pthread_join'
		ret = pthread_join(threadIds[i] , NULL );
		if(ret != 0)
		{

			printf("error joining thread %d\n",(int)threadIds[i]);
		}

		printf("The protected variable value is %ld\n", protVariable);

		ret = pthread_mutex_destroy(&cntr_mutex);
		if(ret != 0)
		{

			printf("couldn't destroy the mutex.\n");
		}

	}

	return 5;
}

I looked at my code properly but I could not find error.
Thanks in advance!

nadroj · 03-06-2010, 10:14 PM

Quote:

Originally Posted by http://opengroup.org/onlinepubs/007908799/xsh/pthread_create.html

int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
void *(*start_routine)(void*), void *arg);

From this, argument 3 should be a pointer to a function of the form

Code:

void * foo(void* bar)

but your passing it "myThread", which has signature

Code:

void myThread(void *arg)

So change return type from "void" to "void*", and of course add the "return" logic in the function.

For the "undefined reference" errors this usually means you're not linking to the library that contains the actual object code. It depends on your compiler, which you haven't told us, but for "gcc" I think you can pass "-pthread" as an argument when compiling. This should get rid of the second "undefined reference" error also.

gozlemci · 03-07-2010, 05:19 AM

Quote:

Originally Posted by nadroj

From this, argument 3 should be a pointer to a function of the form

Code:

void * foo(void* bar)

but your passing it "myThread", which has signature

Code:

void myThread(void *arg)

So change return type from "void" to "void*", and of course add the "return" logic in the function.

For the "undefined reference" errors this usually means you're not linking to the library that contains the actual object code. It depends on your compiler, which you haven't told us, but for "gcc" I think you can pass "-pthread" as an argument when compiling. This should get rid of the second "undefined reference" error also.

Thank you for reply.
I am using eclipse cdt as a compiler and ubuntu 9.04 as a operating system. When I compile code with terminal , it worked fine.

nadroj · 03-07-2010, 10:50 AM

It wasn't clear to me. So it's all working for you now or still not?

rjlee · 03-08-2010, 01:46 AM

Quote:

Originally Posted by gozlemci

Hi there;
I've encountered with the same problem in my code with some extra problems.Here are the code :

Code:

...
[SIZE="6"]		//below code gives error: passing argument 3 of ‘pthread_create’ from incompatible pointer type
...
		//below code gives error: undefined reference to `pthread_join'
		ret = pthread_join(threadIds[i] , NULL );
...

I looked at my code properly but I could not find error.
Thanks in advance!

"Undefined reference" is a linker error, not a compiler error. It means that your code is correct (at least syntactically) but GCC can't find the definition of the pthread_create and pthread_join functions.

You probably need to tell gcc to link against the libpthread.so (or libpthread.a) library. The best way to do this is by adding a command-line argument like -lpthread.

Hope that helps,

—Robert J Lee