System Programming Test Practice

find_character.cpp

#include <iostream>
#include <fstream>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <cstring>
#include <cstdio>
#include <sys/stat.h>

using namespace std;

// Use Standard Library
void create_set() {
    unsigned long limit_it = 10000000000;
    ofstream file_output("zeros.txt");

    for (unsigned long i = 0; i < limit_it; i++) {
        if (i % (limit_it / 100) == 0) {
            cout << "I: " << i << endl;
        }
        file_output << 0;
        file_output.flush();
        if (i == limit_it - 10) {
            file_output << 1;
            file_output.flush();
        }
    }

    file_output.close();
}

// Use Syscall - Much Faster in TMPFS[RAMDISK] comparing to standard library call
void create_set_syscall() {
    unsigned long limit_it = 10000000000;
    int fd = open("zeros_syscall.txt", O_RDWR | O_CREAT, S_IRWXU | S_IRWXG | S_IRWXO);
    if (fd == -1) {
        cout << "File open failed" << endl;
        return;
    }
    dup2(fd, STDOUT_FILENO);
    for (unsigned long i = 0; i < limit_it; i++) {
        if (i % (limit_it / 100) == 0) {
            //cout << "I: " << i << endl;

            fflush(stdout);
        }
        printf("0");
        if (i == limit_it - 10) {
            printf("1");
            fflush(stdout);
        }
    }
    close(fd);
}

int main(int argc, char** argv) {
    //create_set_syscall();
    if (argc != 2) {
        cout << "Usage: file_name process_count" << endl;
        return -1;
    }
    int process_count = atoi(argv[1]);
    int fd = open("zeros_syscall.txt", O_RDONLY);
    if (fd == -1) {
        cout << "Something went wrong with open syscall" << endl;
    }
    struct stat st;
    stat("zeros_syscall.txt", &st);
    unsigned long size = st.st_size;
    unsigned long buffer_length = size / process_count;
    if (size % process_count != 0) {
        buffer_length++;
    }

    char *buffer = new char[buffer_length];
    if (buffer == nullptr) {
        cout << "Something went wrong" << endl;
    }

    for (int i = 0; i < process_count; i++) {
        pid_t tmp_pid = fork();
        if (tmp_pid == 0) {
            int read_byte = read(fd, buffer, buffer_length);
            if (read_byte == -1) {
                exit(255);
            }
            for (unsigned long a = 0; a < buffer_length; a++) {
                if (buffer[a] == '1') {
                    cout << "Found 1 on " << getpid()  << endl;
                }
            }
            exit(1);
        }
    }

    int return_value;
    for (int i = 0; i < process_count; i++) {
        wait(&return_value);
        int tmp_return_value = WEXITSTATUS(return_value);
        if (tmp_return_value == 255) {
            cout << "Finished unexpectedly" << endl;
            cout << tmp_return_value << endl;
        } else {
            cout << tmp_return_value << endl;
        }
    }
    close(fd);
    delete[] buffer;
    return 0;
}