C语言读取文件的fseek的问题
用这样的结构struct
{
char name;
long num;
float score;
}stud;
用fwrite 读入了三个数据
zhang shan
89101
89.5
---------------
li si
89102
90.5
---------------
wang wu
89103
71.5
然后通过fseek定位后读出一个数据,程序如下:
#include<stdio.h>
#include<stdlib.h>
int main()
{
struct
{
char name;
long num;
float score;
}stud;
FILE *fp;
int rec_no;
long offset;
if((fp=fopen("c:\\file1","rb"))==NULL)
exit(1);
printf("enter record number that you want:");
scanf("%d",&rec_no); //输入偏位几位
offset = (rec_no-1)*sizeof(stud); //得到偏移量
if(fseek(fp,offset,0)!=0) //给fp定位
{
printf("can't move pointer there.\n");
exit(1);
}
fread(&stud,sizeof(stud),1,fp); //读取该位置上的内容
printf("name:%s\n",stud.name); //输出
printf("num:%ld\n",stud.num);
printf("score:%f\n",stud.score);
fclose(fp);
system("PAUSE");
return 0;
}
为什么我输入6的时候,不会打印出printf("can't move pointer there.\n");这句话呢?
本来就不会出错吧，虽然是rb方式打开的文件。
The End-of-File internal indicator of the stream is cleared after a call to this function, and all effects from previous calls to ungetc are dropped.
要用fseek又想保证不超过文件尾，自己检查就是：
// long size; FILE* fp;
fseek(fp,0,SEEK_END);
size = ftell(fp);
fseek(fp,0,SEEK_SET);
// offset = (rec_no-1)*sizeof(stud);
if (offset >= size) {
// ...
}
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