Segmentation fault at ./ - c

Question

I'm relatively new to C and I'm starting to work with threads and the command line; I just need help with a bit of debugging and error handling. I've run into a segmentation fault every time I try and process the code. It works fine if there is an argument for argv[1]. However, when trying to catch any errors, such as only entering "./example" and nothing else, it finds a segmentation fault.
I have tried variations of the following code to no avail, including looking to see if argc < 1:
int main(int argc, char * argv[]){
pthread_t worker1;
int in;
if(arv[1] == NULL){
printf("ERROR HERE");
}else{
in = strtol(argv[1], &endptr, 10);
}
if(*endptr > in || *endptr == in){
printf("please eneter a number larger than zero");
return EXIT_FAILURE;
}else{
pthread_create(&worker1, NULL, worker, &in);
pthread_join(worker1, NULL);
}
return EXIT_SUCCESS;
}
Below is the current code which I am using, I'm pretty sure it's something small that I'm overlooking. I have never used strtol before and was using atoi before, I have heard it's a better practice to do this. I'm relatively sure the error is in the code provided as when I test the thread function, it works fine; if more is needed please let me know!
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include <time.h>
int main(int argc, char * argv[]){
pthread_t worker1;
int in = strtol(argv[1], &endptr, 10);
if(*endptr > in || *endptr == in){
printf("please eneter a number larger than zero");
return EXIT_FAILURE;
}else{
pthread_create(&worker1, NULL, worker, &in);
pthread_join(worker1, NULL);
}
return EXIT_SUCCESS;
}

Answer 1

You are trying to access an array without doing any kind of bounds checking first:
int main(int argc, char * argv[]){
pthread_t worker1;
int in = strtol(argv[1], &endptr, 10);
...
Who is to say that argv[1] exists? Certainly not your program, because it doesn't check that condition first. Add a check on argc to make sure you are getting the number of arguments you expect before trying to use them.
if (argc > 1) {
int in = strtol(argv[1], &endptr, 10);
}