A Link Error about Pthreads

[rEmir]

Here is the code:

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

void *thread(void *vargp)
{
	printf("Hello World!\n");
	return NULL;
}

int main()
{
	pthread_t tid;
	pthread_create(&tid , NULL , thread ,NULL);
	pthread_join(tid , NULL);
	return 0;
}

When I type "gcc m.c" in the shell,it says
/home/remir/tmp/ccOoOzic.o: In function `main':
m.c.text+0x39): undefined reference to `pthread_create'
m.c.text+0x47): undefined reference to `pthread_join'
collect2: ld returned 1 exit status

How to solve this problem?Thanks!

[likwid]

You have to link it with -lpthread. Including the headers and linking are not the same.

gcc -o whatever whatever.c -lpthread -Wall

I usually do -Wall cause warnings should be on It's a good habit to get into making warning-free code.

[rEmir]

Thanks for your advise.

What if I use the routines in <semaphore.h>?

I'm new guy.

[Franklin52]

Hi,

To use functions as sem_init, sem_wait, sem_trywait you must include <semaphore.h>.

Regards

[rEmir]

But it says
undefined reference to 'sem_init'.

I think I may link it with some options,but I don't know.

[Franklin52]

Can you copy your code and paste it here within code blocks?

Regards

[rEmir]

#include <semaphore.h>

int main()
{
	sem_t m;
	sem_init(&m , 0 , 1);
	return 0;
}

It's simple code.
But it has a link error:
undefined reference to 'sem_init'.

What does mean of "Regards"?Why your two posts in this thread both have this word?
I'm not English speaker,Thanks!

[Franklin52]

Hi,

It's simple code.
But it has a link error:
undefined reference to 'sem_init'.

Use the -lpthread link option.

What does mean of "Regards"?Why your two posts in this thread both have this word?
I'm not Enlish speaker,Thanks!

I'm also not .
Regards is a synonym for greetings.

Regards