FreePascal:单元转换的问题。

Question

当我编译以下代码时，会出现错误。我不明白其中的一些。

码

program Lasagna;

{$mode objfpc}{$H+}

uses
  {$IFDEF UNIX}{$IFDEF UseCThreads}
  cthreads,
  {$ENDIF}{$ENDIF}
  Classes, SysUtils
  { you can add units after this };

{$R *.res}
type
  TVehicle = record
    kindOfVehicle : String[30];
    numberOfWheels : Integer;
    horsePower : Real;
  end;

var
  F: file of TVehicle;
  Vehicle : Array [1..3] of TVehicle;
  index : Integer;

begin
     writeln('A RECORD OF DIFFERENT KIND OF VEHICLES.');
     writeln('---------------------------------------');
     writeln;

     AssignFile(F,'C:/Users/W/Desktop/CarRecord.dat');
     writeln('Searching for file.');
     if FileExists('C:/Users/W/Desktop/CarRecord.dat') then
        begin
          writeln('File found. Opening file.');
          Rewrite(F);
          writeln('File ready.');
          writeln;
          writeln;

          for index:=0 to 3 do
          begin
            writeln('Enter the following details for vehicle no. ',index);
            write('Kind of Vehicle: ');
            readln(Vehicle[index].kindOfVehicle);
            write(F,Vehicle[index].kindOfVehicle);//line 45: this is a string so why do I get an error?**

            {Do NOT use writeln() when writing to random access files.}

            write('Number of Wheels: ');
            readln(Vehicle[index].numberOfWheels);
            write(F,IntToStr(Vehicle[index].numberOfWheels));//line 51: The int is converted to string, so i shouldn't get an error?

            write('Horse Power of Vehicle: ');
            readln(Vehicle[index].horsePower);
            write(F, RealToStr(Vehicle[index].horsePower));//line 55:  
            end;

          writeln('Done. Closing File.');
          CloseFile(F);
        end
     else
         Rewrite(F);
         CloseFile(F);
         writeln('File Not Found.');

     Writeln('Press ANY key to close the program.');
     Readln;
end.

误差

编译Lasagna.lpr

Lasagna.lpr(45,49)错误:不兼容类型: got "ShortString“预期的"TVehicle”

Lasagna.lpr(51,60)错误:不兼容类型: got "AnsiString“预期的"TVehicle”

Lasagna.lpr(55,59)错误:不兼容类型: got "AnsiString“预期"TVehicle”

Lasagna.lpr(70)致命:有3个错误编译模块，停止

Answer 1

在第21行中，您将F声明为“TVehicle文件”。因此，您应该向其写入TVehicle数据，而不是字符串。

Answer 2

在这3种情况下，您尝试将字符串写入F中，而F被声明为TVehicle文件，所以编译器是正确的。

要解决这个问题，您应该将每个字段读入正确类型的变量，用这些变量填充TVehicle类型变量，或者直接使用TVehicle结构的字段并将该变量写入文件。一些类似的东西(我的Pascal有点生疏了，很可能这不会在不接触它的情况下编译)：

var intermediateVehicle : TVehicle;
....
write('Kind of Vehicle: ');
readln(intermediateVehicle.kindOfVehicle);
write('Number of Wheels: ');
readln(intermediateVehicle.numberOfWheels);
write('Horse Power of Vehicle: ');
readln(intermediateVehicle.horsePower);
write(F,intermediateVehicle);

当然，错误检查还需要添加.