Pascal对象：如何做类型化的前向声明？ [英] Pascal Object: how to do a typed forward declaration?

问题描述

我正在将出色的fmod C标头转换为Pascal，并且由于前向声明而陷入困境。
如果我在类型之前声明函数 ，则错误为 FMOD_CODEC_STATE：未知，如果我在函数之前声明FMOD_CODEC_STATE ，则错误为 FMOD_CODEC_METADATACALLBACK：未知
知道如何解决此问题吗？
非常感谢！

I'm translating the great fmod C header to Pascal, and I'm stuck because of a forward declaration. If I declare the function before the type, the error is "FMOD_CODEC_STATE: unknown", and if I declare the FMOD_CODEC_STATE before the function, the error is "FMOD_CODEC_METADATACALLBACK: unknown" Any idea how I could solve this problem? Thank you very much !

type
  FMOD_CODEC_STATE = Record
    numsubsounds: Integer;
    waveformat: array[0..0] of FMOD_CODEC_WAVEFORMAT;
    plugindata: Pointer;

    filehandle: Pointer;
    filesize: Cardinal;
    fileread: FMOD_FILE_READCALLBACK;
    fileseek: FMOD_FILE_SEEKCALLBACK;
    metadata: FMOD_CODEC_METADATACALLBACK;
  end;
  FMOD_CODEC_METADATACALLBACK    = function (codec_state: FMOD_CODEC_STATE; tagtype: FMOD_TAGTYPE; name: PChar; data: Pointer; datalen: Cardinal; datatype: FMOD_TAGDATATYPE; unique: Integer):FMOD_RESULT;

推荐答案

记录不需要按值传递。实际上，原始的C代码始终不会按值传递它。它通过参考传递并带有一个指针。声明指针，然后声明函数，然后声明记录：

The record doesn't need to be passed by value. In fact, the original C code doesn't pass it by value anyway. It's passed by reference, with a pointer. Declare the pointer, then the function, and then the record:

type
  PFMOD_CODEC_STATE = ^FMOD_CODEC_STATE;
  FMOD_CODEC_METADATACALLBACK = function (codec_state: PFMOD_CODEC_STATE; tagtype: FMOD_TAGTYPE; name: PChar; data: Pointer; datalen: Cardinal; datatype: FMOD_TAGDATATYPE; unique: Integer):FMOD_RESULT;
  FMOD_CODEC_STATE = Record
    numsubsounds: Integer;
    waveformat: PFMOD_CODEC_WAVEFORMAT;
    plugindata: Pointer;

    filehandle: Pointer;
    filesize: Cardinal;
    fileread: FMOD_FILE_READCALLBACK;
    fileseek: FMOD_FILE_SEEKCALLBACK;
    metadata: FMOD_CODEC_METADATACALLBACK;
  end;

是的，您可以在声明某物之前声明一个指向某物的指针至。不过，您不允许转发声明记录，因此，上面给出的顺序是这三个声明的唯一可能的顺序。

Yes, you're allowed to declare a pointer to something before you've declared the thing it points to. You're not allowed to forward-declare records, though, so the order given above is the only possible order for those three declarations.

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