c - Get/Set the pthread scheduling policy in Linux -

the code below sample provided book in operating systems course. when compiling error shown below it.

#include <pthread.h> #include <stdio.h> #define num_threads 5  int main(int argc, char *argv[]) {     int i, policy;     pthread_t tid[num_threads];     pthread_attr_t attr;      pthread_attr_init(&attr);      if(pthread_attr_getschedpolicy(&attr, &policy) != 0)         fprintf(stderr, "unable policy.\n");     else{         if(policy == sched_other)             printf("sched_other\n");         else if(policy == sched_rr)             printf("sched_rr\n");         else if(policy == sched_fifo)             printf("sched_fifo\n");     }      if(pthread_attr_setschedpolicy(&attr, sched_fifo) != 0)         fprintf(stderr, "unable set policy.\n");     /* create threads */     for(i = 0; < num_threads; i++)         pthread_create(&tid[i], &attr, runner, null);     /* join on each thread */     for(i = 0; < num_threads; i++)         pthread_join(tid[i], null); }  /* each thread begin control in function */ void *runner(void *param) {     /* work... */      pthread_exit(0); } 

i compiled using command...

gcc linux_scheduling.c -o scheduling 

however, error.

linux_scheduling.c:32:34: error: 'runner' undeclared (first use in function)    pthread_create(&tid[i], &attr, runner, null);                                ^ linux_scheduling.c:32:34: note: each undeclared identifier report once each function appears in 

i tried adding -pthread:

gcc linux_scheduling.c -o scheduling -pthread 

but error remains.

thanks help!

you have correct compiling command:

gcc linux_scheduling.c -o scheduling -pthread 

but need put:

void *runner(void *param); 

ahead of start of main declare it:

#include <pthread.h> #include <stdio.h> #define num_threads 5  void *runner(void *param);  int main(int argc, char *argv[]) {     ...