Hi everybody!

Years ago I used Delphi (on Windows) to access a C or C++ API (for talking directly with embedded device) and I can remember that there were a number of gotchas (e.g. the calling convention had to be changed form Pascal to something else (extern?) etc. ).

Now I am wondering about writing a simple Lazarus GUI to the Telegram API (all C header files, AFAICT) on Linux (and maybe Windows, if not too difficult to port). Any gotchas to keep in mind for using C and C++ libraries from Lazarus/Free Pascal (on Linux and maybe Windows) or good guides?

Thanks
Chavoux
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Basically: use cdecl calling convention (on Windows it *might* be stdcall though), do not use Pascal types like classes, strings, etc. for accessing the C API, better use the types in the ctypes unit instead.

Additional help is available here:

http://wiki.freepascal.org/Creating_bindings_for_C_libraries

Regards,
Sven

El 06/03/14 20:31, Chavoux Luyt ha escrit:

Take a look here
ftp://ftp.freepascal.org/fpc/docs-pdf/CinFreePascal.pdf

and here
http://wiki.lazarus.freepascal.org/Creating_bindings_for_C_libraries

Bye

Chavoux Luyt wrote

Years ago I used Delphi (on Windows) to access a C or C++ API

You can't access a C++ API.

-Michael

You can't access a C++ API.

Not yet. But it is planned for the future:

http://freepascal.org/future.var
"Linking with C++ code"

And with quite some restrictions it already works, see $fpc/tests/test/cg/tcppcl{1,2}.pp.

Regards,
Sven

Thanks everybody!

The two links were just what I needed. And some parts were faintly familiar. :-)

Cheers
Chavoux
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Is this feature at trunk?

Further examples of use.. ?

I haven't worked on it since some time, so the current state is even in 2.6.0.

Further examples of use.. ?

A cppclass is declared like this:

=== code begin ===

type
   TTest = cppclass external 'MyCLib' name 'Test' (TParent)
     procedure Test;
     class procedure StaticTest;
   end;

=== code end ===

Notes:
- if TParent is defined it needs to be a cppclass as well
- for sizeof to work correctly you need to specifiy the fields the same way as in C++ (though this might still be buggy)
- cppclass instances are not implicit pointers like classes, so you need to use "myvar^.Test" instead

Current restrictions:
- currently no namespaces supported
- currently no support for virtual metods (static methods work, instance methods *should* work)
- no support for construction/destruction yet (so you need to have the library instantiate the object)
- no support for multiple inheritance or virtual inheritance
- no support for operators (especially not the C++ specific ones)

In general this feature is experimental/in development, so your mileage may vary. Bug reports are welcome though :)

Regards,
Sven