C语言中fflush等函数的用法

 

示例: fflush.c

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

int writefile(char *filename, char *buf, int length)
{
    FILE *fp;
    int j = 0;
    size_t i = 0;
    fp = fopen(filename, "w");
    if (fp == NULL) {
        printf("\topen file error!\n");
        return -1;
    } else {
        while (length != 0) {
            i = fwrite(&buf[j], 1, 1, fp);
            length--;
            j ;
        }
    }
    fflush(fp);
    fclose(fp);
    return 0;
}

int readfile(char *filename, char *buf)
{
    FILE *fp;
    int j = 0;
    size_t i;
    fp = fopen(filename, "rb");
    if (fp == NULL) {
        printf("error\n");
        return -1;
    } else {
        while (1) {
            i = fread(&buf[j], 1, 1, fp);
            if (i == 0)
                break;
            j ;
        }
    }
    fflush(fp);
    fclose(fp);
    return 111;
}
int main(int argc, char **argv)
{
    char msg[128] = "hello,xiong feng!";
    char fbuf[1024] = "";
    char *filename = "/xiongfeng";
    int w_ret = 0;
    int r_ret = 0;

    w_ret = writefile(filename, msg, strlen(msg));
    if (w_ret < 0) {
        printf("Write file %s fail!\n", filename);
    }
    printf("msg:%s\n", msg);    // 如果在未加入fflush(fp), 该输出有可能不能正常输出,特别是在perl调用该程序时, perl不能获取该程序中的输出

    r_ret = readfile(filename, fbuf);
    if (r_ret < 0) {
        printf("Read file %s fail!\n", filename);
    }
    printf("fbuf:%s\n", fbuf);   // 这行同上面的: printf("msg:%s\n", msg);
    return 0;
}

网上还有二次封装的fflush的函数, 如下:

void flush(FILE *stream)
{
     int duphandle;

     /* flush the stream's internal buffer */
     fflush(stream);

     /* make a duplicate file handle */
     duphandle = dup(fileno(stream));

     /* close the duplicate handle to flush/
        the DOS buffer */
     close(duphandle);
}

下面是这两个函数的分析:

dup():
int   dup(int   handle);
作用：复制一个文件句柄

fileno():

示例：fileno.c:

#include <stdio.h>
int main(int argc, char **argv)
{
    FILE *fp;
    int fd;
    fp = fopen("/xiongfeng", "r");
    fd = fileno(fp);
    printf("fd = %d\n", fd);
    fclose(fp);
    return 0;
}
运行结果: fd = 3