c++ 写文件性能比较

cpp 复制代码

#include <iostream>
#include <fstream>
#include <vector>
#include <chrono>
#include <glog/logging.h>
using milli = std::chrono::milliseconds;

int main()
{
    int num = 1000000000;
    int* arr = new int[num];
    std::ofstream outfile("data.bin", std::ios::binary | std::ios::out);
    std::vector<int> tmp;

    if (!outfile.is_open())
    {
        std::cerr << "Failed to open the file." << std::endl;
        // return 1;
    }

    auto start = std::chrono::high_resolution_clock::now();
    for (int i = 0; i < num; i++)
    {
        outfile.write(reinterpret_cast<const char *>(&i), sizeof(i));
    }
    auto end = std::chrono::high_resolution_clock::now();
    std::cout << "直接写入文件耗时："<<(float)std::chrono::duration_cast<milli>(end - start).count()
              << " milliseconds\n";

    start = std::chrono::high_resolution_clock::now();
    for (int i = 0; i < num; i++)
    {
        tmp.push_back(i);
    }
    outfile.write(reinterpret_cast<const char *>(tmp.data()), sizeof(int) * tmp.size());
    end = std::chrono::high_resolution_clock::now();
    std::cout << "放入vector再写入文件: "<<(float)std::chrono::duration_cast<milli>(end - start).count()
              << " milliseconds\n";

    start = std::chrono::high_resolution_clock::now();
    for (int i = 0; i < num; i++)
    {
        arr[i] = i;
    }
    outfile.write(reinterpret_cast<const char *>(arr), sizeof(int) * num);
    end = std::chrono::high_resolution_clock::now();
    std::cout << "预设内存块, 赋值写入："<<(float)std::chrono::duration_cast<milli>(end - start).count()
              << " milliseconds\n";

    outfile.close();
}

编译执行

bash 复制代码

(py37) hq@nuc:~/tmp/hq$ g++ test.cpp -lglog
(py37) hq@nuc:~/tmp/hq$ ./a.out 
直接写入文件耗时：12037 milliseconds
放入vector再写入文件: 11278 milliseconds
预设内存块, 赋值写入：8115 milliseconds

结论：预设内存，一次性写入新能最高