关于C的fgets

[liveNight365]

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

void main()
{
     /* 打开模式介绍
       "r"   只读,文件必须存在
       "r+", 读写,文件必须存在

       "w"   只写,不管文件是否存在,都创建新文件(同时清空原内容)
       "w+", 读写,不管文件是否存在,都创建新文件(同时清空原内容)

       "a"   追加,   文件不存在会创建新文件,存在则打开.只能追加
       "a+", 读+追加,文件不存在会创建新文件,存在则打开.可以调整文件指针来读取数据,但是写入数据会自动跳到文件最后进行追加
     */
    FILE *pFile;
    pFile = fopen("a.txt", "w");
    fprintf(pFile, "fclose example");
    rewind(pFile);
    fputs("1234567890 hello world 你好啊\nsecond line\ngo\n", pFile);
    fclose(pFile);

    // 以读写方式打开一个文件
    pFile = fopen("a.txt", "a+"); //1,打开一个文件,不存在在创建
    if (pFile == NULL)
    {
        puts("fopen error\n");
    }
    else
    {
        //pFile = freopen("a.txt", "r+", pFile);  //重新打开这个文件,以r+(可读写)方式打开
        fclose(pFile);
        pFile = fopen("a.txt", "r+");
        if (pFile == NULL)
        {
            puts("freopen error\n");
        }
        else
        {
            char buff[1024] = {0};
            fgets(buff, 1023, pFile);  //遇到文件结束符或者换行符就会停止读取.
            puts(buff);
        }
    }

    //rewind(pFile);
    int pos = ftell(pFile);
    fpos_t fpos;
    fgetpos(pFile, &fpos); 
    if (pos == EOF)
    {
        puts("ftell is end of file\n");
    }
    fseek(pFile, 0, SEEK_CUR); //SEEK_SET, SEEK_CUR, SEEK_END.....注意,注释了这一句后,后面的fputs就没有写到文件中去.
    fputs("new fputs", pFile);
    fputc('A',  pFile);
    fflush(pFile);

    printf("\n\nfgetc测试\n");
    rewind(pFile); //移动文件指针到文件头
    int ch;
    while (EOF != (ch=fgetc(pFile)))
    {
        putchar(ch);
    }

    struct stTest
    {
        int    a;
        char   c;
        double d;
    };
    stTest st = {1, 'C', 3.65};
    fseek(pFile, 0, SEEK_END);
    fwrite(&st, sizeof(st), 1, pFile);
    memset(&st, 0, sizeof(st));
    fseek(pFile, -sizeof(st), SEEK_END);
    fread(&st, sizeof(st), 1, pFile);
    printf("%d, %c, %Lf", st.a, st.c, st.d);
   
    fclose(pFile);
    system("pause");
 }

[liveNight365]

上面的代码第55行.为什么.求指点。

[liveNight365]

void test1()
{
    FILE *pFile;
    pFile = fopen("a.txt", "w");
    fputs("1234567890 hello world 你好啊\nsecond line\ngo\n", pFile);
    fclose(pFile);

    pFile = fopen("a.txt", "r+");
    char buff[1024] = {0};
    fgets(buff, 1023, pFile);  //遇到文件结束符或者换行符就会停止读取.
    puts(buff);

    fseek(pFile, 0, SEEK_CUR); //SEEK_SET, SEEK_CUR, SEEK_END.....注意,注释了这一句后,后面的fputs就没有写到文件中去.
    fputs("new fputs", pFile);
    fputc('A',  pFile);
    fflush(pFile);

    rewind(pFile); //移动文件指针到文件头
    int ch;
    while (EOF != (ch=fgetc(pFile)))
    {
        putchar(ch);
    }

    fclose(pFile);
    system("pause");
}

简化版本,大家帮忙看看问题啊

[mujiok2003]

For files open for update (those which include a "+" sign), on which both input and output operations are allowed, the stream should be flushed (fflush) or repositioned (fseek, fsetpos, rewind) between either a writing operation followed by a reading operation or a reading operation which did not reach the end-of-file followed by a writing operation.

[liveNight365]

引用 3 楼 mujiok2003 的回复:

For files open for update (those which include a "+" sign), on which both input and output operations are allowed, the stream should be flushed (fflush) or repositioned (fseek, fsetpos, rewind) between either a writing operation followed by a reading operation or a reading operation which did not reach the end-of-file followed by a writing operation.

原来如此.搞定。

[zhangsha3121]

每天回贴可得分!