Exam

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

#define PERMS 0666

int main() {
    int fd_source, fd_target;
    char buffer[4096];
    char filename_source[] = "src";
    char filename_target[] = "dst";
    ssize_t cread, cwrite;
    char *out_ptr = buffer;
    pid_t pid1 = fork();
    if(!pid1) {
        if((fd_source = open(filename_source, O_RDONLY)) < 0) {
            perror("open source file error");
        }
        if((fd_target = open(filename_target, O_CREAT | O_WRONLY, PERMS)) < 0 ) {
            perror("open target file error");
        }
        while((cread = read(fd_source, buffer, sizeof buffer)) > 0) {
            do {
                if((cwrite = write(fd_target, out_ptr, cread)) >= 0) {
                    cread -= cwrite;
                    out_ptr += cwrite;
                } else {
                    break;
                }
            } while(cread > 0);
        }
        close(fd_source);
        close(fd_target);
        exit(0);
    }
    wait(NULL);
}