Change value of a struct - c

Question

I was learning how to use multithreading and I had a question with an exercise that I had come across.
How can I change the bool value of the structure to be true using the function? (I'm bad with pointers). The lock should be in the main function.
The purpose is to lock a thread and prevent others from executing once that state is reached.
pd: I use pthreads
typedef struct Data{
bool used;
}data;
void lock(data *info){
info -> used = true;
}

Answer 1

Use the & operator to get the address of an object. The address is the pointer to the object.
typedef struct Data{
bool used;
}data;
void lock(data *info){
info -> used = true;
}
int main(int argc, char *argv[])
{
data my_struct = {0};
lock(&my_struct);
if (my_struct.used == true)
printf("It is true!\n");
return 0;
}

Answer 2

My understanding of your situation is that you want use pthread locks in your lock function to guard the write operation (info->used = true).
You should create the pthread_mutex_t (Data structure for locking) before using the lock(data *) function. Following is an example.
#include <stdio.h>
#include <stdbool.h>
#include <pthread.h>
typedef struct data
{
bool used;
}data;
pthread_mutex_t spin_lock;
void* lock(void *xxinfo)
{
if (xxinfo != NULL)
{
data *info= (data *)xxinfo;
pthread_mutex_lock(&spin_lock);
info->used = true;
printf("Set the used status\n");
pthread_mutex_unlock(&spin_lock);
}
return NULL;
}
pthread_t threads[2]; // Used it for demonstrating only
int main()
{
int status = 0;
data some_data;
if(0 != pthread_mutex_init(&spin_lock, NULL))
{
printf("Error: Could not initialize the lock\n");
return -1;
}
status = pthread_create(&threads[0], NULL, &lock, &some_data);
if (status != 0)
{
printf("Error: Could not create 0th thread\n");
}
status = pthread_create(&threads[1], NULL, &lock, &some_data);
if (status != 0)
{
printf("Error: Could not create 1st thread\n");
}
pthread_join(threads[0], NULL);
pthread_join(threads[1], NULL);
pthread_mutex_destroy(&spin_lock);
return 0;
}
In this example I am using global spin_lock (which is not a great idea). In your code consider keeping it in an appropriate scope. I have created two threads here for demonstration. To my understanding they don't race at all. I hope this gives you an idea to use pthread locks in your case. You should use lock just for the part of the code that modifies or reads the data.
Note that you should create lock <pthread_mutex_init> before creating the threads. You can also send the locks as parameter to the thread.
Destroy the lock after using it.