#include <stdio.h>
#include <sys/mman.h>
#include <sys/wait.h>
#include <unistd.h>

int main()
{
    void* address = mmap(nullptr, PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_SHARED, -1, 0);
    if (address == MAP_FAILED)
    {
        perror("mmap");
        return 1;
    }

    int* ptr = (int*)address;
    *ptr = 16;

    pid_t child = fork();
    if (child < 0)
    {
        perror("fork");
        return 1;
    }
    if (child == 0)
    {
        *ptr = 32;
        _exit(0);
    }

    waitpid(child, NULL, 0);

    printf("the value is %d\n", *ptr);

    return 0;
}