c - 为什么 fseek 在这里不返回位置，而只是将 fread 重定向到特定记录？

Question

所以我基本上有一个包含一些学生及其信息的二进制输入文件夹。在“while”函数之后，我不明白关于 fseek 和 fread 的一些事情。在我运行它并键入一个键来搜索学生之后，它会打印与该键关联的学生，而不是该位置上的那个（以字节为单位的维度作为偏移量）。我想知道为什么，为了将这些信息用于我的项目，因为这个程序是教授的一种教程。先感谢您！

*编辑（第二个程序是我对该项目的尝试，但使用汽车。它的输出是位置“chooseKey”的汽车，而不是作为第一个程序的“chooseKey”作为属性。我不知道我做错了什么.)

   #include <stdio.h> 
   #include <conio.h> 

typedef struct { 

                 int nrm;             
                 char CNP[14];         
                 char nume[30];      
                 int an;              
                 int grupa;           
                 unsigned char note[20];  
                 char is;
               } STUDENT;

int filesize(FILE* f, int rec_size)
{
  long crt_pos;
  int size;

  crt_pos = ftell(f);  
  fseek(f, 0, SEEK_END) ;    
  size=ftell(f) / rec_size;  
  fseek(f, crt_pos, SEEK_SET); 
  return size; 

}

void main()
{ char numefr[30] = "Studenti_r_f.dat";
  FILE* f;
  STUDENT x;
  int key, dim;

  fopen_s(&f, numefr, "rb+");
  dim=filesize(f, sizeof(STUDENT)); 

  printf_s("Enrollment number: ");
  scanf_s("%d", &key);
  while(key != 0)
  {
    //check key range
    if(key >= dim)
      printf_s("\nThere is no student with this enrollment number. Try again?");
    else
    {
      //check if valid key
      fseek(f, key*sizeof(STUDENT), SEEK_SET);
      fread(&x, sizeof(STUDENT), 1, f);
      if(x.is == 0)
        printf("\nThere is no student with this enrollment number. Try again?");
      else
        printf_s("\nStudent: %s, Year: %d, Group: %d, ATP grade: %d\n",x.nume,x.an,x.grupa,x.note[5]);
    }
    printf_s("\n\nEnrollment number (or 0): ");
    scanf_s("%d", &key);
  }

 fclose(f);

 printf("\nDone. Press a key.",numefr);
 _getch();
}

typedef struct {
    int key;
    char color[20];
    int price;
    char brand[15];
}CAR ;

int sizeOfFile(FILE* inBinFile, int sizeOfRecord)
{
    long currentPosition;
    int size;

    currentPosition = ftell(inBinFile);
    fseek(inBinFile, 0, SEEK_END);
    size = ftell(inBinFile) / sizeOfRecord;
    fseek(inBinFile, currentPosition, SEEK_SET);
    return size;
}
void main()
{
    FILE * inBinFile;
    CAR var;
    int chooseKey, fileDim;

    printf_s("Type a key to identify a car..."); // 20 records in the file
    scanf_s("%d", &chooseKey); 

    fopen_s(&inBinFile, "Machines.bin", "rb+");
    fileDim = sizeOfFile(inBinFile, sizeof(CAR));

    while (chooseKey != -1)
    {
        if (chooseKey >= fileDim)
            printf_s("\nNo car with key %d found. Retry.", chooseKey);
        else
        {
            fseek(inBinFile, chooseKey*sizeof(CAR), SEEK_SET);
            fread(&var, sizeof(CAR), 1, inBinFile);
            printf_s("\nThe %d key indicates to the %s car coloured in %s which cost %d dollars", chooseKey, var.brand, var.color, var.price);
        }
        printf_s("\n\n\nTo search for another car enter a key, or hit 1 and enter to stop: ");
        scanf("%d", &chooseKey);
    }
    fclose(inBinFile);
    printf_s("\nAlright. Press any key...");
    _getch();
}   ```

标签： cfilebinaryfreadfseek