#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>

#define BUFFSIZE 8

int main() {

    extern int errno;

    char file_read[] = "f_read.txt";
    char file_write[] = "f_write.txt";
    
    char buffer[BUFFSIZE];
    bzero(buffer, sizeof(buffer));

    // opening files

    int desc_fr = open(file_read, O_RDONLY);
    if (desc_fr < 0) {
        perror("ERROR opening f_read.txt");
        exit(errno);
    }

    int desc_fw = open(file_write, O_WRONLY | O_CREAT | O_TRUNC, 0640);
    if (desc_fw < 0) {
        perror("ERROR opening f_write.txt");
        exit(errno);
    }

    // reading and writing to buffer

    int ret_write = 0;
    int ret_read = BUFFSIZE;
    while (ret_read == BUFFSIZE) {
        ret_read = read(desc_fr, buffer, BUFFSIZE);
        if (ret_read < 0) {
            perror("ERROR reading f_read.txt");
            exit(errno);
        }

        printf("[%d] %.*s\n", ret_read, ret_read, buffer);

        ret_write = write(desc_fw, buffer, ret_read);
        if (ret_write < 0) {
            perror("ERROR writing to f_write.txt");
            exit(errno);
        }

        bzero(buffer, sizeof(buffer));
    }

    // closing files

    int ret_close = 0;
    ret_close = close(desc_fr);
    if (ret_close < 0) {
        perror("ERROR closing f_read.txt");
        exit(errno);
    }
    close(desc_fw);
    if (ret_close < 0) {
        perror("ERROR closing f_write.txt");
        exit(errno);
    }

    return EXIT_SUCCESS;
}