如何将C/C++程序转译成Delphi(十一)

最新推荐文章于 2021-07-28 15:16:07 发布

原创最新推荐文章于 2021-07-28 15:16:07 发布 · 919 阅读

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文章标签：

#delphi #translation #macros #constants #function #documentation

博客主要讨论了C宏到Delphi的翻译问题。由于Delphi中没有宏，需用函数来翻译C宏。多数情况下，依据文档信息翻译宏比直接翻译代码更简单。还指出有时无法实现C代码与Delphi翻译的一一对应，如声明常量时的宏处理，建议将宏整体翻译成函数。

4. Macros

In C it's possible to define macros. Macros are not available in Delphi, so functions must be used to translate C-macros. In most cases it's easier to translate a macro based on the information about it from the documentation than trying to translate the code directly.

One example of a macro:

#define PRIMARYLANGID(lgid) ((WORD )(lgid) & 0x03ff)

Here, quite clearly, the macro accepts integers. A valid translation of this macro is

Function PRIMARYLANGID (lgid: DWord): DWord;



Begin



  Result := lgid and $03FF



End;

The following macro accepts any datatype as parameter:

#define max(a,b)            (((a) > (b)) ? (a) : (b))

It compares the values of parameter a with parameter b and returns the higher value. So that our function can pass any datatype, we can use variants.

Function Max (A, B: Variant): Variant;



Begin



  If A > B then



    Result := A



  else



    Result := B



End;

I do recommend implementing the Delphi translation on the basis of the macro's documentation.

Sometimes it is not possible to translate macros so that there is a 1:1 correspondence between the C code and the Delphi translation.

For example, some header files use macros in #define statements for declaring constants.

Here is an example from the clusapi header file.

#define CLUSPROP_SYNTAX_VALUE( type, format ) ((DWORD) ((type << 16) | format))

The ensuing declarations use a macro named CLUSTER_PROPERTY_SYNTAX to calculate the values of the constants:

typedef enum CLUSTER_PROPERTY_SYNTAX {



  CLUSPROP_SYNTAX_ENDMARK = CLUSPROP_SYNTAX_VALUE( CLUSPROP_TYPE_ENDMARK, CLUSPROP_FORMAT_UNKNOWN ),

    CLUSPROP_SYNTAX_NAME  = CLUSPROP_SYNTAX_VALUE( CLUSPROP_TYPE_NAME, CLUSPROP_FORMAT_SZ ),

    CLUSPROP_SYNTAX_RESCLASS = CLUSPROP_SYNTAX_VALUE( CLUSPROP_TYPE_RESCLASS, CLUSPROP_FORMAT_DWORD ),

We cannot do it like this in Delphi and, besides, Delphi does not allow the value of an enumeration entry to be assigned. The macro must be resolved in order to do the translation to Delphi.

We can translate the #define statement into the following Delphi function:

Function CLUSPROP_SYNTAX_VALUE (dwType: DWORD; dwFormat: DWORD): DWORD;

Begin

  Result := (dwType shl 16) or dwFormat;

End;

However, function calls are not possible in constant declarations. To resolve that, we declare the constants as follows, without wrapping them together as the C macro抯 enumeration has done:

CONST 

  CLUSPROP_SYNTAX_ENDMARK = CLUSPROP_TYPE_ENDMARK shl 16 or CLUSPROP_FORMAT_UNKNOWN;

  CLUSPROP_SYNTAX_NAME  = CLUSPROP_TYPE_NAME shl 16 or CLUSPROP_FORMAT_SZ;

  CLUSPROP_SYNTAX_RESCLASS = CLUSPROP_TYPE_RESCLASS shl 16 or CLUSPROP_FORMAT_DWORD;

Actually, this is a case where I would recommend translating the macro as a whole into a function, as it might be useful to make it available to applications.

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