io redirect_ioredirect

前言

和别人讨论问题，说到IO重定向。只有在低版本vs中, 替换_iob[]的方法。
win版，可以用freopen来实现IO重定向.
linux版，可以用dup2来实现IO重定向.
如果能使用API来进行IO重定向，那兼容性好多了. 代码实现也优雅的多:)

win版实验

// @file io_redirect.cpp
// @brief io redirect to file, env is vs2017

#include "stdafx.h"
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#define _CRT_SECURE_NO_WARNINGS
#pragma warning(disable : 4996)

#ifndef MAXBYTE
#define MAXBYTE 0xff
#endif // #ifndef MAXBYTE

#define LOG_FILE_PATH_NAME "d:\\my_log.txt"

FILE* g_fp_log_file = NULL;
FILE* g_fp_stdout_org = NULL;
FILE* g_fp_stdout_new = NULL;

void log_init();
void log_uninit();
int main_proc(int argc, char** argv);
void show_file_content(const char* psz_file_path_name);

int main(int argc, char** argv)
{
    printf(">> main\r\n");
    system("del d:\\my_log.txt");

    log_init();
    main_proc(argc, argv); // this print on file
    log_uninit();

    // this print on console
    printf(">> ---------- d:\\my_log.txt ----------\r\n");
    show_file_content(LOG_FILE_PATH_NAME);
    printf("<< ---------- d:\\my_log.txt ----------\r\n");
    printf("<< main\r\n");
    system("pause");

    /* run result on consle
    >> main
    >> log_init
    << log_uninit
    >> ---------- d:\my_log.txt ----------
    << log_init
    argc = 1
    argv[0] = D:\ls_RE\prj\study\linux_prj\printf_redirect\win\x64\Debug\printf_redirect.exe
    >> log_uninit
    << ---------- d:\my_log.txt ----------
    << main
    请按任意键继续. . .
    */

    return 0;
}

void log_init()
{
    printf(">> log_init\r\n");

    // 用替换_iob[]中的FILE*不通用,高版本vs没有_iob
    // printf use stdout as io handle
    // #define stdout (__acrt_iob_func(1))
    //  _ACRTIMP_ALT FILE* __cdecl __acrt_iob_func(unsigned _Ix);
    /*
        #ifndef _FILE_DEFINED
        #define _FILE_DEFINED
        typedef struct _iobuf
        {
        void* _Placeholder;
        } FILE;
        #endif
    */

    // 用freopen兼容性很好
    g_fp_stdout_org = stdout;
    g_fp_log_file = freopen(LOG_FILE_PATH_NAME, "a+", stdout);
    if (NULL == g_fp_log_file) {
        printf("error : can't io redirect stdout\r\n");
    }

    printf("<< log_init\r\n");
}

void log_uninit()
{
    printf(">> log_uninit\r\n");
    if (NULL != g_fp_log_file) {
        fflush(stdout);
        fclose(g_fp_log_file);
        g_fp_log_file = NULL;

        g_fp_stdout_new = freopen("CON", "w", stdout);
        if (NULL == g_fp_stdout_new) {
            printf("error : can't io redirect stdout\r\n");
        }
    }
    printf("<< log_uninit\r\n");
}

int main_proc(int argc, char** argv)
{
    int i = 0;

    printf("argc = %d\r\n", argc);
    for (i = 0; i < argc; i++) {
        printf("argv[%d] = %s\r\n", i, argv[i]);
    }

    return EXIT_SUCCESS;
}

void show_file_content(const char* psz_file_path_name)
{
    FILE* fp = NULL;
    char sz_buf[4096] = { '\0' };

    do {
        if (NULL == psz_file_path_name) {
            break;
        }

        fp = fopen(psz_file_path_name, "r");
        if (NULL == fp) {
            break;
        }

        do {
            memset(sz_buf, 0, sizeof(sz_buf));
            if (NULL == fgets(sz_buf, (int)sizeof(sz_buf), fp)) {
                break;
            }

            printf("%s", sz_buf);
        } while (1);
    } while (0);

    if (NULL != fp) {
        fclose(fp);
        fp = NULL;
    }
}
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linux版实验

// @file io_redirect.cpp
// @brief io redirect to file, env is debian7.5

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

#ifndef MAXBYTE
#define MAXBYTE 0xff
#endif // #ifndef MAXBYTE

#define LOG_FILE_PATH_NAME "/var/log/my_log.txt"

int g_fd_stdout_dup = -1;
FILE* g_fp_log_file = NULL;

void log_init();
void log_uninit();
int main_proc(int argc, char** argv);
void show

int main(int argc, char** argv)
{
    printf(">> main\r\n");
    system("rm /var/log/my_log.txt");

    log_init();
    main_proc(argc, argv); // this print on file
    log_uninit();

    // this print on console
    printf(">> ---------- /var/log/my_log.txt ----------\r\n");
    system("cat /var/log/my_log.txt");
    printf("<< ---------- /var/log/my_log.txt ----------\r\n");
    printf("<< main\r\n");

    /* run result on consle
    >> main
    >> ---------- /var/log/my_log.txt ----------
    argc = 1
    argv[0] = ./case_io_redirect
    << ---------- /var/log/my_log.txt ----------
    << main
    */

    return 0;
}

void log_init()
{
    int fd_stdout = -1;
    int fd_log_file = -1;

    g_fp_log_file = fopen(LOG_FILE_PATH_NAME, "a+");
    if (NULL != g_fp_log_file) {
        if (-1 == g_fd_stdout_dup) {
            g_fd_stdout_dup = dup(STDOUT_FILENO);
        }

        fd_log_file = fileno(g_fp_log_file);
        fd_stdout = dup2(fd_log_file, STDOUT_FILENO);
    }
}
void log_uninit()
{
    if (NULL != g_fp_log_file) {
        fflush(stdout);
        fclose(g_fp_log_file);
        g_fp_log_file = NULL;
    }

    if (-1 != g_fd_stdout_dup) {
        dup2(g_fd_stdout_dup, STDOUT_FILENO);
        close(g_fd_stdout_dup);
        g_fd_stdout_dup = -1;
    }
}

int main_proc(int argc, char** argv)
{
    int i = 0;

    printf("argc = %d\r\n", argc);
    for (i = 0; i < argc; i++) {
        printf("argv[%d] = %s\r\n", i, argv[i]);
    }

    return EXIT_SUCCESS;
}
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