Can't make thread from a function in another file [closed] - c

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I have two files. sim.c and devices.c.
Here's the sim.c
...
#include "devices.h"
int main(int argc, char **argv) {
pthread_t *tid;
tid = (pthread_t *) malloc(sizeof(pthread_t) * 3);
// this is where I start the 3 threads located in devices.c
if (pthread_create(&tid[0], NULL, device_one, NULL)) {
exit(1);
}
if (pthread_create(&tid[1], NULL, device_two, NULL)) {
exit(1);
}
if (pthread_create(&tid[2], NULL, device_three, NULL)) {
exit(1);
}
// wait for 3 threads to finish
int i;
for (i = 0; i < 3; i++) {
if (pthread_join(tid[i], NULL)) {
exit(1);
}
}
}
Here's devices.c
...
#include "devices.h"
extern void *device_one(void *arg) {
printf("device one is called\n");
return NULL;
}
extern void *device_two(void *arg) {
printf("device two is called\n");
return NULL;
}
extern void *device_three(void *arg) {
printf("device three is called\n");
return NULL;
}
And here's devices.h
#ifndef DEVICES_H
#define DEVICES_H
extern void *device_one(void *arg);
extern void *device_two(void *arg);
extern void *device_three(void *arg);
However, when I compile, I get 3 errors under sim.c saying
undefined reference to 'device_one'
undefined reference to 'device_two'
undefined reference to 'device_three'

Answer 1

The errors suggest you are not linking with the devices module when compiling sim.c (which contains main). You could compile as:
gcc sim.c devices.c -I.
Or you can create a makefile:
CC = gcc
CFLAGS = -I.
DEPS = devices.h
OBJ = sim.o devices.o
LDLIBS = -pthread
%.o: %.c $(DEPS)
$(CC) -c -o $# $< $(CFLAGS)
sim: $(OBJ)
$(CC) -o $# $^ $(CFLAGS) $(LDLIBS)
.PHONY: clean
clean:
rm -rf $(OBJ)