C程序读写文件

#include <stdio.h>
#include <string.h>
int main ()
{
    FILE *fp;
    char msg[]="20161203";
    char buf[200];
    fp = fopen("f:\\操作系统\\commandlist.txt","r+");
    if (NULL == fp)
    {
        printf("The file doesn't exist!\n");
        return -1;
    } 
    fseek(fp,10L,SEEK_SET);//定位文件指针到文件开始位置
    fwrite(msg,strlen(msg),1,fp);//把字符串内容写入到文件
    fread(buf,strlen(msg),1,fp);//把文件内容读入到缓存
     buf[strlen(msg)] = '\0';//删除缓存内多余的空间![图片描述][1]
    return 0;
}

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