io benchmarking for C++

//C++ Headers
#include <iostream>
#include <fstream>
#include <vector>
#include <charconv>
#include <random>
#include <chrono>

//C Headers
#include <cstdlib>
#include <cstring>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <cstdio>
#include <fcntl.h>
#include <unistd.h>
using namespace std;
using namespace chrono;

const size_t COUNT = 10000000; //Write 10M ints to disk in ASCII format

void die(string s) {
    cerr << s << endl;
    exit(EXIT_FAILURE);
}

int main() {
    //Generate some random numbers
    auto start = steady_clock::now();
    using data_type = uint32_t;
    vector<data_type> vec;
    vec.reserve(COUNT);
    default_random_engine gen;
    uniform_int_distribution<data_type> rando;
    for (size_t i = 0; i < COUNT; i++) vec.push_back(rando(gen)); //Emplace_back doesn't change the time
    duration <double, milli> dur = steady_clock::now() - start;
    cout << "Random vector generation time: " << dur.count() << "ms\n";

    //Create a buffer with all the data converted into it to minimize write calls
    start = steady_clock::now();
    const size_t DIGITS = 11; //10 digits + newline needed for each int, max
    const size_t SIZE = COUNT * DIGITS; //Bytes in the array
    char *buffer = new char[SIZE];
    char *ptr = buffer; //Pointer to where we're writing to the array
    char *end = buffer + sizeof(char) * SIZE; //Pointer to one past the end of the array
    for (auto i : vec) {
        ptr = to_chars(ptr,end,i).ptr; //We're ignoring the error condition, which should be fine
        *ptr++ = '\n'; //Write a newline at the end and advance the pointer one char
    }
    duration <double, milli> buf_dur = steady_clock::now() - start;
    cout << "Buffer conversion time: " << buf_dur.count() << "ms\n";

    //Benchmark fprintf
    start = steady_clock::now();
    FILE *file1 = fopen("fprintf.txt", "w");
    for (auto i : vec) fprintf(file1, "%u\n", i);
    fclose(file1);
    dur = steady_clock::now() - start;
    cout << "Fprintf time: " << dur.count() << "ms\n";

    //Benchmark fstream
    ofstream file2("fstream.txt");
    start = steady_clock::now();
    //for (auto i : vec) file2 << i << endl; //Don't do this, it is 10-20x slower
    for (auto i : vec) file2 << i << '\n';
    file2.close();
    dur = steady_clock::now() - start;
    cout << "Fstream time: " << dur.count() << "ms\n";

    //Benchmark syscall write time
    start = steady_clock::now();
    int file3 = creat("fsyscall.txt", S_IRWXU); //syscall to open a file, returns a file descriptor (int)
    size_t bytes_written = static_cast<size_t>(ptr-buffer);
    size_t result = write(file3, buffer, bytes_written);
    if (!result) die("We need this since the header files don't like you discarding the result\n");
    close(file3); //syscall to close a file
    dur = steady_clock::now() - start;
    cout << "Syscall write time (with buffer): " << dur.count() + buf_dur.count() << "ms\n";

    //Benchmark fprintf with a buffer
    start = steady_clock::now();
    FILE *file4 = fopen("fprintf2.txt", "w");
    fprintf(file4, "%s", buffer);
    fclose(file4);
    dur = steady_clock::now() - start;
    cout << "Fprintf time (with buffer): " << dur.count() + buf_dur.count() << "ms\n";

    //Benchmark fstream with a buffer
    start = steady_clock::now();
    ofstream file5("fstream2.txt");
    file5 << buffer;
    file5.close();
    dur = steady_clock::now() - start;
    cout << "Fstream time (with buffer): " << dur.count() + buf_dur.count() << "ms\n";

    //Benchmark mmap files with a buffer
    start = steady_clock::now();
    int file6 = open ("fsyscall2.txt", O_RDWR | O_CREAT | O_TRUNC, 0x0777);
    if (file6 == -1) die("Open file6 failed\n");
    auto retval = lseek(file6,bytes_written-1,SEEK_SET); //Make a 0 byte file...
    if (retval == -1) die("Lseek failed\n");
    retval = write(file6, "", 1); //...really big by writing to what will be the end
    if (retval != 1) die("Write failed\n");
    char *file_array = (char *)mmap (0, bytes_written, PROT_READ | PROT_WRITE, MAP_SHARED, file6, 0); //Treat file as array
    if (file_array == MAP_FAILED) die("Mmap error");
    memcpy (file_array, buffer, bytes_written); //Copy files to disk
    munmap(file_array,bytes_written); //Unmap file
    close(file6);
    dur = steady_clock::now() - start;
    cout << "Mmap time (with buffer): " << dur.count() + buf_dur.count() << "ms\n";

    delete[] buffer;
}