如何有条件地编译较新的Indy功能？ [英] How to conditionally compile a newer Indy feature?

问题描述

我已经找到有关如何在运行时检查Indy版本的此答案不同的方式。但是，我正在寻找如何在编译时使用条件语句检查Indy版本。较新版本的Indy中有一项功能，我希望我的开源项目能够使用此功能。但是我需要有条件地对其进行编译。

I've already found this answer on how to check the Indy version at run-time, and there are multiple different ways. However I'm looking how to use conditionals to check the Indy version at compile-time. There's a feature in newer versions of Indy, and I want my open-source project to use this feature if it's available. But I need to conditionally compile it.

我发现 IdVers.inc ，但是此文件仅包含常量-没有版本条件。

I've found IdVers.inc, but this file only contains constants - no version conditionals.

更具体地说， TIdHTTP 具有属性 HTTPOptions ，其中有一个新选择 hoWantProtocolErrorContent 。如果可用，我想使用它。

More specifically, the TIdHTTP has a property HTTPOptions which has a new choice hoWantProtocolErrorContent. If this is available, I'd like to use it.

如果可用，如何有条件地使用此选项？

How can I conditionally use this option if it's available?

推荐答案

我认为您可以使用$

I think you can get the result you're wanting to achieve using the

{$if declared ...

构造。在rtl的SysInit.Pas中有一个使用示例：

construct. There is an example of its usage in SysInit.Pas in the rtl:

function GetTlsSize: Integer;
{$IF defined(POSIX) and defined(CPUX86) and (not defined(EXTERNALLINKER))}
asm
        // Use assembler code not to include PIC base gain
        MOV  EAX, offset TlsLast
end;
{$ELSE}
begin
  Result := NativeInt(@TlsLast);
  {$IF DECLARED(TlsStart)}
  Result := Result - NativeInt(@TlsStart);
  {$ENDIF}
  [...]

我在评论中提到的文章 $如果声明了，
D2009联机帮助。

As well as the article I mentioned in a comment, $If Declared, there is also this in the D2009 online help.

$如果已声明可使用类方法，例如

procedure TMyClass.DoSomething;
begin
  {$if declared(TMyClass.Added)}  // Added being a procedure of TMyClass
  Added;
  {$endif}
end;

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