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fopen vs. freopen speed
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| #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(); | |
| } | |
Author
cybertxt
commented
Sep 19, 2017
open/close纳入计时也是一样效果。
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