Undefined reference to pthread_create in Linux?

Question

I picked up the following demo off the web from https://computing.llnl.gov/tutorials/pthreads/ #include <pthread.h> #include <stdio.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); } } pthread_exit(NULL); }But when I compile it on my machine (running Ubuntu Linux 9.04) I get the following error: corey@ubuntu:~/demo$ gcc -o term term.c term.c: In function ‘main’: term.c:23: warning: incompatible implicit declaration of built-in function ‘exit’ /tmp/cc8BMzwx.o: In function `main': term.c:(.text+0x82): undefined reference to `pthread_create' collect2: ld returned 1 exit statusThis doesn't make any sense to me, because the header includes `pthread.h`, which should have the `pthread_create` function. Any ideas what's going wrong?

Answer 1

You need to include the library e.g.

gcc -lpthread file.c