HELP in a Thread code

[full_adder]

Hi everyone

I wrote the following code from an OS book. But when I compiled it the following msg had appeared:

In function 'main': undefined reference to 'pthread_create'
In function 'main': undefined reference to 'pthread_join'

I don't understand what it means exactly!!

#include<pthread.h>
#include<stdio.h>
int sum;
void* runner(void *param);
int main(int argc, char *argv[]){
	pthread_t tid;
	pthread_attr_t attr;

	if(argc !=2){
		printf("usage: a.out <int value>\n");
		return -1;
	}
	if( atoi(argv[1]) < 0 ){
		printf("%d must be >= 0\n",atoi(argv[1]));
		return -1;
	}
	pthread_attr_init(&attr);
	pthread_create(&tid,&attr,(void *)runner,(void *)argv[1]);
	pthread_join(tid,NULL);

	printf("sum = %d\n",sum);
}
void* runner(void *param){
	int i, upper=atoi(param);
	sum=0;
	for(i=1;i<=upper;i++)
		sum +=i;
	pthread_exit(0);
}

[tempora]

compile this code in the following way

gcc code.c -lpthread

where code.c is assumed to be the filename of your c code.


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