OS LAB 4 LIN

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>

int main() {
    char buffer[256] = "";
    struct flock lock = {F_WRLCK, SEEK_SET, 0, 0, getpid()};//from start (0) 'til end (0) of file
    int opened = open("./forlab4.txt", O_RDWR);
    if (opened != -1) {
        if (fcntl(opened, F_SETLK, &lock) == -1) {
            system("clear");
            printf("\033[9B\033[15C\033[91mLocking is unavailable yet.\n\033[25CWaiting.\n");//\n is needed as it flushes stdout immediately instead of end of programm
            fcntl(opened, F_SETLKW, &lock);
        }
        system("clear");
        printf("\033[9B\033[15C\033[91mFile is successfully locked.\033[39m\n");

        int len;
        len = read(opened, buffer, 255);
        write(1, buffer, len);

        sleep(7);
        fcntl(opened, F_UNLCK, &lock);
        system("clear");
        printf("\033[9B\033[14C\033[91mFile is successfully unlocked.\n");

        close(opened);
        return 0;
    } else {
        system("clear");
        printf("\033[9B\033[17C\033[91mFile can not be opened.\n\033[11CProgram will be terminated shortly.\n");
    }
    printf("\033[39m");
    return 0;
}