20121011總結——文件操作函數：rewind(fp) - fseek(fp, offset, seek_set) - ftell(fp)

說明：
        rewind () 函數，
        fseek (fp, offset, seek_set) 函數，
        ftell (fp) 函數。
       

程序附錄：
/* Description: the test of function
 *         rewind()
 *         fseek(fp, offset, seek_set)
 *         ftell(fp)
 * Time:    2012.10.11
 * Author:    essencelite


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

int main()
{
    FILE * fp;
    char *ps = "fseek(), fsetpos() return 0, and ftell() returns the current offset. \
            Otherwise,  -1  is returned and errno is set to indicate the error.";
    int length = strlen(ps);
    
/* creat re.txt and copy content to re.txt */
    fp = fopen("re.txt", "w");
    if (fp == NULL) {
        perror("fopen re.txt error\n");
        exit(EXIT_FAILURE);
    }
    int ret = fwrite(ps, 1, length, fp);
    printf("ret = %d \n",ret);
    fclose(fp);








/*---------------------------------------rewind()-------------------------------------------
 * description: set the fp to the start of the file
 *-----------------------------------------------------------------------------------------*/

/* test the rewind() function */
    int i = 0;
    char ch = 0;

    fp = fopen("re.txt", "r");
    if (fp == NULL) {
        perror("fopen error\n");
        exit(EXIT_FAILURE);
    }
    for(i = 0; i < 10; i++) {
        ch = fgetc(fp);
        printf("_%c_", ch);
    }
    printf("\n");

    rewind(fp);
    ch = fgetc(fp);
    printf("ch = %c \n", ch);

    fclose(fp);








/*--------------------------------fseek(fp, offset, seek_set)-------------------------------
 * description:    set the fp to point to the station (seek_set+offset);
 *         from "seek_set" to "seek_set + offset", fp point to the (seek_set+offset);
 * example:    fseek(fp, 10L, 8)  which means:from 8 to 18; fp point to the 18;
 *         the offset can be negative;  
 * parameters:    set = 0, stand the start of file;
 *         cur, stand current station;
 *         END, stand end of the file;
 *-----------------------------------------------------------------------------------------*/

/* test the fseek(fp, offset, seek_set) function */
    i = 0;
    ch = 0;
    fp = fopen("re.txt", "r");
    if (fp == NULL) {
        perror("fopen error\n");
        exit(EXIT_FAILURE);
    }

    fseek(fp, 10L, 0);
/* -------------------------------------ftell(fp)------------------------------------------
 *description: location the current station of the fp
 *---------------------------------------------------------------------------------------*/

/* test the ftell() function */
    long tell = ftell(fp);
    printf("after 10 offset form ,the current fp station, tell = %d \n", tell);
    printf("\n");

    fclose(fp);



    return 0;
}