Printing out even and odd numbers using thread in C - c

Question

#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
#include <stdlib.h>
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
void* thread_even(void* arg);
void* thread_odd(void* arg);
int main(int argc, char** argv) {
pthread_t tid[2];
pthread_create(&tid[0], 0, &thread_even, 0);
pthread_create(&tid[1], 0, &thread_odd, 0);
pthread_join(tid[0], NULL);
pthread_join(tid[1], NULL);
return 0;
}
void* thread_even(void* arg) {
int* thread_id = (int*)arg;
pthread_mutex_lock(&mutex);
for(int i = 1; i <= *thread_id; i++)
{
if(i%2 != 0)
{
printf("Thread 1: %d", i);
}
}
pthread_mutex_unlock(&mutex);
return NULL;
}
void* thread_odd(void* arg) {
int* thread_id = (int*)arg;
pthread_mutex_lock(&mutex);
for(int i = 1; i <= *thread_id; i++)
{
if(i%2 == 0)
{
printf("Thread 2: %d", i);
}
}
pthread_mutex_unlock(&mutex);
return NULL;
}
The above is the code I am working on but I get a segment fault error... What I want to achieve is, for example,
when I compile it and run with an argument 8 (./number 8)
it should print out
thread 1: 1
thread 2: 2
thread 1: 3
... etc till the number, 8.
in which thread 1s should represent the even numbers and the thread 2s stand for the odd numbers.
Please help... I want to develop my knowledge about C but have no one to ask..
Thanks.

Answer 1

Looks like you are passing 0 AKA NULL to the last parameter of pthread_create, and then doing the following:
int* thread_id = (int*)arg;
pthread_mutex_lock(&mutex);
for(int i = 1; i <= *thread_id; i++)
So, thread_id will certainly be NULL, referencing it will be a SEGFAULT.
If you want to pass an upper bound for each thread to run to, do you can do something like this:
int main(int argc, char** argv) {
pthread_t tid[2];
int *ids = malloc(2 * sizeof(int));
ids[0] = 10; /* upper bound for thread 1 */
ids[1] = 10; /* upper bound for thread 2 */
pthread_create(&tid[0], 0, &thread_even, &ids[0]);
pthread_create(&tid[1], 0, &thread_odd, &ids[1]);
pthread_join(tid[0], NULL);
pthread_join(tid[1], NULL);
free(ids);
return 0;
}
There are ways to do this without resorting to heap allocation, but this is the most straight forward.