使用不同模式的文件进行C编程？

Question

#include<stdio.h>
int main()
{
    FILE *fp;
    char buff[255];

    fp=fopen("test.txt","w");

    printf("File test.txt in w mode\n");
    fprintf(fp,"Template string 1:\n");

    fputs("Template string 2:",fp);
    printf("File test.txt is created at local path\n\n");
    fclose(fp);

    fp=fopen("test.txt","r");
    printf("\n\nFile test.txt in r mode\n");
    fscanf(fp,"%s",buff);
    printf("The content of the file test.txt using fscanf() is:\n%s\n",buff);

    fgets(buff,255,(FILE *)fp);
    printf("The content of the file test.txt using fgets() is :\n%s\n",buff);

    fgets(buff,255,(FILE *)fp);
    printf("The content of the file using fgets() is :\n%s\n",buff);
    fclose(fp);

    fp=fopen("test.txt","a");
    printf("\n\nFile test.txt in a mode\n");
    fprintf(fp,"Template String 3:\n");
    fgets(buff,255,(FILE *)fp);
    printf("After append %s\n",buff);
    fclose(fp);

    fp=fopen("test.txt","r+");
    printf("File test.txt in r+ mode\n");
    fgets(buff,255,(FILE *)fp);
    printf("\n\nThe content of the file test.txt in r+ mode is:\n%s\n",buff);
    fclose(fp);
}

我有上面的代码，我理解。我怀疑当我追加字符串＆＃34;模板字符串3：＆＃34;我的fp将内容添加到文件末尾的文件test.txt，添加fp之后应该指向文件末尾（我希望）但是如果我使用fgets来读取文件的内容fp到它应该拥有的buff。任何人都可以解释此时发生的事情。

Answer 1

C库函数char *fgets(char *str, int n, FILE *stream)从指定的流中读取一行并将其存储到str指向的字符串中。当读取（n-1）个字符，读取换行符或达到文件结尾时（以先到者为准），它会停止。

这就是为什么代码的最后一部分只显示文件的第一行。你没有获得printf("After append %s\n",buff);输出的原因是此时文件指针位于EOF。

当您cat文件时，您会看到所有行都在那里。