compare_istream_readers.cpp

#include <vector>
#include <iostream>
#include <fstream>
#include <cstring>
#include <cerrno>
#include <chrono>
#include <string>

using std::chrono::time_point;
using std::chrono::microseconds;
using std::chrono::duration_cast;

namespace {
    std::vector<uint8_t> read_entirely_manual(const std::string& pth) {
        std::ifstream strm{pth, std::ios::binary};
        strm.exceptions(std::ifstream::badbit);
        
        constexpr size_t read_sz = 8192;
        std::vector<uint8_t> out(read_sz);
        auto bytes_read = 0;
        while (strm.read(reinterpret_cast<char*>(out.data() + bytes_read), read_sz)) {
            auto count = strm.gcount();
            bytes_read += count;
            out.resize(out.size() + count);
        }
        bytes_read += strm.gcount();
        out.resize(bytes_read);

        return out;
    }

    std::vector<uint8_t> read_entirely_clean(const std::string& pth) {
        auto strm = std::ifstream{pth, std::ios::in | std::ios::binary};
	strm.exceptions(std::ifstream::failbit);
	return std::vector<std::uint8_t>(std::istreambuf_iterator<char>{strm}, {});
    }
}

int main(int argc, char** argv) {
    int num_paths = argc - 1;
    char** paths = argv + 1;
    
    for (int i = 0; i < num_paths; i++) {
        const char* path = paths[i];

        auto manual_start = std::chrono::high_resolution_clock::now();
        std::vector<uint8_t> manual = read_entirely_manual(path);
        auto manual_dur =
            duration_cast<microseconds>(std::chrono::high_resolution_clock::now() - manual_start);

        auto clean_start = std::chrono::high_resolution_clock::now();
        std::vector<uint8_t> clean = read_entirely_clean(path);
        auto clean_dur =
            duration_cast<microseconds>(std::chrono::high_resolution_clock::now() - clean_start);

        if (manual != clean) {
            throw std::runtime_error{"outputs do not match: implementations differ!"};
        }

        std::cout << path << " " << manual.size() << " manual " << manual_dur.count() << ", clean " << clean_dur.count() << std::endl;
    }    

    return 0;
}