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Howto create C-Header for Delphi/Free Pascal/Lazarus DLL – data types – Stack Overflow

Posted by jpluimers on 2021/09/23

From a long time ago, but got a request for it a while ago is [WayBack/Archive.is] Howto create C-Header for Delphi/Free Pascal/Lazarus DLL – data types – Stack Overflow:

I have used the below construct to generate header files compatible with the C-mode compiler of Visual C++ 6 from Delphi 5 code when Delphi had the -JPH switch (see notes below).
Note that I have not used this since Delphi 5, but the switch has since then been expanded:
Somewhere along the line, the [WayBackJPHNE switch has been added to the dcc32 command-line compiler:
  -JPHNE = Generate C++ .obj file, .hpp file, in namespace, export all
It certainly does not handle all types, and you will need quite a bit of [Archive.isHPPEMIT and [Archive.isEXTERNALSYM directives.
It generates the .hpp files to import the DLL that was written in Delphi.
Notes from the Delphi 5 era:
{ Visual C++ 6 does not like nested structs/unions the way that BC++ can handle them.
  Visual C++ 6 requires the "typedef" to be present AND the typename AFTER the struct definition.
  You will see this when defining TConversationId, TReturnKey and other types that depend on nested structs/unions

  The trick is to perform these steps each and every time this unit changes:
    - Generate this unit once with all the EXTERNALSYM disabled.
      - Then the DCC32 -JPH will generate the basic structs for them.
    - Copy all the nested struct and union definitions to this file
    - Embed the definitions with (*$HPPEMIT '' *)
    - Append the typename at the end of the struct definition
    - Enable all the EXTERNALSYM again
    - Regenerate the HPP files by using DCC32 -JPH
  To make this process easier, we have introduced two new conditional defines:
    - BCB - disable EXTERNALSYM, disable HPPEMIT
    - VC6 - enable EXTERNALSYM, enable HPPEMIT

  A similar thing is with these constructions that VC6 does not like those either:
    - short strings (BCB defines them as "SmallString<##>" which VC6 does not like).
    - short integers (BCB defines them as "Shortint" so we have included an HPPEMIT for that)
}

{$ifdef win32}
  { important! Makes sure that the all enumerated types fit in exactly one byte each! }
  {$Z1}

  { force the C/C++ HPP header files to have the C/C++ compiler pack structure elements on byte boundaries }
  {$ifdef BCB}
    {$HPPEMIT '#pragma option push -a1' }
  {$endif BCB}
{$endif win32}

And the download (hopefully I have converted it to git by then):

The link to the converter is now [Archive.is] bitbucket.org/jeroenp/wiert.me/src/default/Native/… – Delphi Coder

–jeroen

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