FPC:记录中的RTTI [英] FPC : RTTI on records

问题描述

这是我第一次访问此网站.通常，我不会在旧帖子中找到回复，但是我并没有解决我的实际问题.

This is my first time on this site. Usually, I have no problem to found replies in the old posts but I don't success with my actual problem.

我想知道如何使用RTTI函数在运行时知道Lazarus/FPC下记录的属性/成员?我知道如何为一个类(持久性后代和已发布的属性)执行此操作，但对于FPC则不行.一些链接指示如何在Delphi(自D2010)下进行此操作，但我不知道如何在Lazarus下进行转置.

I would like to know how use RTTI functions to know at running time the properties/members of a record under Lazarus/FPC? I know how to do it for a class (Tpersistent descendant and published properties) but not for FPC. Some links indicates how to do it under Delphi (From D2010), but I don't know how to transpose it under Lazarus.

在此先感谢您的帮助和协助. 萨利姆·拉里布(Salim Larhrib).

Thanks in advance for help and assistance. Salim Larhrib.

致敬:如我之前所说，这是我的第一个要求.但是我明白.你说的对.这是我的代码

To kevin : As I told before, this is my first demand. But I understand. You are right. This is my code

procedure TMainForm.btRecordTHashListClick(Sender: TObject);
var
  pTData    : PTypeData;
  pTInfo    : PTypeInfo;
  TablePtr  : PatableRecord;
  Loop      : Integer;
begin
  // Set of Record pointers + HashList

  // Create Container
  if  not Assigned(FTableRecList) then FTableRecList := TFPHashList.Create;

  // Insert data
  new(TablePtr);
  TablePtr^.description := 'Dictionnaire des tables.';
  FTableRecList.add('atable', TablePtr );

  new(TablePtr);
  TablePtr^.description := 'Dictionnaire des fonctions.';
  FTableRecList.add('afunction', TablePtr );

  new(TablePtr);
  TablePtr^.description := 'Dictionnaire des listes d''option.';
  FTableRecList.add('alist', TablePtr );

  // Read records
  for Loop:=0 to FTableRecList.Count-1 do
  begin
    TablePtr := FTableRecList[Loop];
    ShowMessage('Parcours Index : ' + TablePtr^.description);
  end;

  // Find records
  try
    TablePtr := FTableRecList.Find('ddafunction');
    ShowMessage('Record finded : ' + TablePtr^.description);
  except
    ShowMessage('Not such record .');
  end;
  try
    TablePtr := FTableRecList.Find('afunction');
    ShowMessage('Record finded : ' + TablePtr^.description);
  except
    ShowMessage('No such record.');
  end;

  // Free memory : To put later in TFPHashList wrapper
  for Loop:=0 to FTableRecList.Count-1 do Dispose(PatableRecord(FTableRecList[Loop]));

// RTTI
  pTInfo := TypeInfo(TatableRecord);

  pTData := GetTypeData(pTInfo);
  ShowMessage('Member count = '+IntToStr(pTData^.PropCount));
end;

推荐答案

警告:它适用于FPC 2.7.1或更高版本.

您可以使用指针处理记录字段.这是示例:

You can deal with record fields using pointers. Here is example:

program rttitest;

uses
    TypInfo;

type
    TMyRec = record
        p1: Integer;
        p2: string;
    end;

var
    td: PTypeData;
    ti: PTypeInfo;
    mf: PManagedField;
    p: Pointer;
    f: Pointer;

    r: TMyRec;

begin
    r.p1 := 312;
    r.p2 := 'foo-bar';

    ti := TypeInfo(r);
    td := GetTypeData(ti);

    Writeln(td^.ManagedFldCount); // Get count of record fields

    // After ManagedFldCount TTypeData contains list of the TManagedField records
    // So ...
    p := @(td^.ManagedFldCount); // Point to the ManagedFldCount ...
    // Inc(p, SizeOf(Integer)); // Skip it (Wrong for 64-bit targets)
    // Next line works for both
    Inc(p, SizeOf(td^.ManagedFldCount)); // Skip it

    mf := p; // And now in the mf we have data about first record's field
    Writeln(mf^.TypeRef^.Name);

    Write(r.p1); // Current value
    f := @r;
    Inc(f, mf^.FldOffset); // Point to the first field
    Integer(f^) := 645; // Set field value
    Writeln(r.p1); // New value

    // Repeat for the second field
    Inc(p, SizeOf(TManagedField));
    mf := p;
    Writeln(mf^.TypeRef^.Name);

    Write(r.p2);
    f := @r;
    Inc(f, mf^.FldOffset);
    string(f^) := 'abrakadabra';
    Writeln(r.p2);


    Readln;
end.

这篇关于FPC:记录中的RTTI的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！