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C++ multithreading code does not compile

Posted on 2013-01-16
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Last Modified: 2013-01-16
Hello experts!

I am using ubuntu and geanie.
I try to compile following code:


/******************************************************************************
* FILE: hello.c
* DESCRIPTION:
*   A "hello world" Pthreads program.  Demonstrates thread creation and
*   termination.
* AUTHOR: Blaise Barney
* LAST REVISED: 08/09/11
******************************************************************************/
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#define NUM_THREADS      5

void *PrintHello(void *threadid)
{
   long tid;
   tid = (long)threadid;
   printf("Hello World! It's me, thread #%ld!\n", tid);
   pthread_exit(NULL);
}

int main(int argc, char *argv[])
{
   pthread_t threads[NUM_THREADS];
   int rc;
   long t;
   for(t=0;t<NUM_THREADS;t++){
     printf("In main: creating thread %ld\n", t);
     rc = pthread_create(&threads[t], NULL, PrintHello, (void *)t);
     if (rc){
       printf("ERROR; return code from pthread_create() is %d\n", rc);
       exit(-1);
       }
     }

   /* Last thing that main() should do */
   pthread_exit(NULL);
}


I get error messages:


g++ -Wall -o "main" "main.cxx" (in directory: /home/jacek/Documents/cpp/wlasne/MultiThreading/4)
/tmp/ccvE3G41.o: In function `main':
main.cxx:(.text+0x85): undefined reference to `pthread_create'
collect2: ld returned 1 exit status
Compilation failed.

What do I do wrong?

Thank you

panJames
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Question by:panJames
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4 Comments
 
LVL 31

Accepted Solution

by:
Zoppo earned 1500 total points
ID: 38783034
Hi panJames,

I guess you need to link 'pthread' library into your program. Try adding -lpthread to the command line ...

Hope that helps,

ZOPPO
0
 

Author Comment

by:panJames
ID: 38783126
g++ -Wall -o -lpthread "main" "main.cxx" (in directory: /home/jacek/Documents/cpp/wlasne/MultiThreading/4)
g++: error: main: No such file or directory
Compilation failed.
0
 

Author Comment

by:panJames
ID: 38783131
g++ -Wall -o -lpthread "%e" "%f"
0
 
LVL 31

Expert Comment

by:Zoppo
ID: 38783141
Hi,

you should not add this directly after -o. The argument after -o is the name of the resulting executable.

ZOPPO
0

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