德尔福错误E2064左侧无法分配

Question

我发现了一些用于创建midi文件的旧代码.在较新的Delphi中,它给了我无法分配错误.我假设一个Unicode问题？但是如何解决呢？这些行给出了错误

    midCmd[2] := $90;
    midCmd[3] := Note;
    midCmd[4] := Velocity;

如果需要,这里有完整的程序

    procedure SaveAsMidi(note: byte; FileName: string);
    const // MIDI file header
      midHdr: array[0..13]of byte =
      ($4D,$54,$68,$64, //[0..3] Always MThd
      $00,$00,$00,$06,  // [4..7] Always the same
      $00,$01,          // [8..9] Two bytes for file format
                        // $01 = synchronous multiple tracks
      $00,$01,          // [10..11] Two bytes for number of tracks
      $01,$E0);         // [12..13] Two bytes for ticks per quarter note
      // MIDI track header
      midTrk: array[0..7]of byte =
      ($4D,$54,$72,$6B, // [0..3] Always MTrk
      $00,$00,$00,$0E); // [4..7] Four bytes for track size in bytes
      // MIDI track end bytes
      midEnd: array[0..3]of byte =
      ($00,$FF,$2F,$00); // [0..3] Always the same
      // MIDI command
      midCmd: array[0..4]of byte =
      ($80,$00,          // [0..1] Two bytes for time in ticks
      $90,               // [2] Command:
                         // $90 = Note on at channel 0
                         // $80 = Note off at channel 0
      $00,$00);          // [3] Note and [4] velocity
      // Constant velocity
      Velocity=$FF;
      // Constant duration
      Time=$FF;
var  midFile: TFileStream;
begin
     // Create MIDI file
     midFile := TFileStream.Create(FileName +'.mid', fmCreate);
     with midFile do try
    // Write MIDI header
    Write(midHdr, SizeOf(midHdr));
    // Write MIDI track
    Write(midTrk, SizeOf(midTrk));
    // Write Note On
    // Play immediately = time is 0
    midCmd[2] := $90;
    midCmd[3] := Note;
    midCmd[4] := Velocity;
    Write(midCmd, SizeOf(midCmd));
    // Write Note Off
    // Separate time into two bytes
    midCmd[0] := $80 or (Time div 128 mod 128);
    midCmd[1] := $00 or (Time mod 128);
    midCmd[2] := $80;
    Write(midCmd, SizeOf(midCmd));
    // Write MIDI track end
    Write(midEnd, SizeOf(midEnd));
  finally
    midFile.Free;
  end;
end;

将字节$ FF格式分配给字节数组需要什么语法？谢谢你的帮助.

Answer 1

您已声明midcmd为类型化常量,并且{$WRITEABLECONST}编译器指令(现在)处于默认状态{$J-}(或更详细:){$WRITEABLECONST OFF},这意味着类型化常量不可写.

在Delphi和Object Pascal的早期版本中,类型常量总是可写的,这可以解释你在网上找到的代码.或者,它可能已经特别声明编译器指令为{$J+}(或{$WRITEABLECONST ON}).

要按原样使用代码,请更改指令.要保留默认指令,请将键入的常量midcmd更改为变量(将其移动到该var部分).

您可以在Embarcadero的文档中阅读有关可写类型常量的内容.