fopen vs. freopen speed

write_speed_test.cpp

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <time.h>
#include <assert.h>

#ifdef _WIN32
#include <Windows.h>
#else
#include <unistd.h>
#endif

clock_t do_write(FILE* fp, char* data, size_t len) {
    // The clock() function returns an approximation of processor time used by the program.
    // The  value  returned is the CPU time used so far as a clock_t;
    // to get the number of seconds used, divide by CLOCKS_PER_SEC.
    clock_t clock_begin, clock_end;
    clock_begin = clock();
    for (int i = 0; i < 1000; ++i) {
        auto n = fwrite(data, len, 1, fp);
        assert(n == 1);
    }
    fflush(fp);
    clock_end = clock();

    return clock_end - clock_begin;
}

int main() {
    auto data = new char[1048576]; // 1MB
    auto cache = new char[512 * 1024];

    // initialize the buffer
    for (int i = 0; i < 1048576; ++i)
        data[i] = i;

    clock_t elapsed;
    
    auto fp_reopen = freopen("data_freopen.bin", "wb", stdout);
    assert(fp_reopen != nullptr);
    setvbuf(fp_reopen, cache, _IOFBF, 512 * 1024);
    elapsed = do_write(fp_reopen, data, 1048576);

    // redirect stdout to console
#ifdef _WIN32
    freopen("CONOUT$", "w", stdout);
#else
    freopen("/dev/tty", "w", stdout);
#endif

    printf("write with freopen clocks elapsed: %zu\n", elapsed);

#ifdef _WIN32
    Sleep(10000);
#else
    sleep(10)
#endif

    auto fp = fopen("data_fopen.bin", "wb");
    assert(fp != nullptr);
    setvbuf(fp, cache, _IOFBF, 512 * 1024);
    elapsed = do_write(fp, data, 1048576);
    fclose(fp);
    printf("write with fopen clocks elapsed: %zu\n", elapsed);

    delete[] data;
    delete[] cache;

    getchar();
}

参考： http://www.cnblogs.com/vertextao/p/7560157.html