fseek

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// FSeek.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include "stdio.h"
#include "string.h"
#include "iostream.h"

#define STU_NUM 100

struct STU
{
int id;
double score;
char name[20];
};

void MakeFile()
{
FILE * fp = fopen("c://stu.dat","wb");

for(int i=0;i<STU_NUM; i++)
{
STU stu;
memset(&stu,0,sizeof(STU));

  stu.id =i;
  stu.score = i+0.01*i;
  strcpy(stu.name,"hello");

fwrite(&stu,sizeof(STU),1,fp);
}

fclose(fp);

}

int GetRecordCount()
{
FILE *fp = fopen("c://stu.dat","rb");

fseek(fp,0,SEEK_END);

int len = ftell(fp);

int nCount = len / sizeof(STU);

printf("文件记录总数为:%d/n",nCount);

fclose(fp);

return nCount;

}
void Read(int nIndex)
{

FILE *fp = fopen("c://stu.dat","rb");

fseek(fp,nIndex * sizeof(STU),SEEK_SET);

STU stu;

memset(&stu,0,sizeof(STU));

fread(&stu,sizeof(STU),1,fp);

printf("记录为：【id::%d - score::%.2f - name::%s】/n",stu.id,stu.score,stu.name);

fclose(fp);

}

int main(int argc, char* argv[])
{
MakeFile();

int nCount = GetRecordCount();

while(nCount > 0)
{
int nIndex;

  cout << "/n 输入学号读取对应学生记录，输入 -1 结束：/n";

  cin >> nIndex;
  if(nIndex <0 )
  {
   break;
  }

  if(nIndex > nCount)
  {
   printf("范围超出/n");

   continue;
  }

Read(nIndex);

}

return 0;
}