I'm working on wrapping a C library that has a function that can handle a variable number of parameters. What mechanism can I use in FPC to call this correctly?

The C prototype for the function looks like this:

void QMCall(char * subrname, short int argc, ...);

The function can handle up to 20 parameters after the 'argc' parameter. Would I have to define all 20 possible parameters? Each of the optional parameters is a string type.

Thanks for the help!

g.

procedure QMCall(subrname: pchar; argc: shortint; rest: array of
const); cdecl; external;

You can then call it using

QMCall('test',1,['para1','para2',5,null]);

(I know you said it only needed strings, but it's just to show that you can pass anything that way, just like with "...").

Jonas

I have no idea. I've never programmed in Delphi in my entire life.

Jonas

Jonas, thanks for the quick response! Do you know if this same trick will work with Delphi 7?

Thanks again!

g.

Sorry, it should be

procedure QMCall(SubrName : PChar; ArgCount : shortint; const Args :
array of
const); cdecl; external 'QMClient';

(i.e., another "const" in front of "Args").

Jonas

My declaration reads like this:

procedure QMCall(SubrName : PChar; ArgCount : shortint; Args : array of
const); cdecl;
  external 'QMClient';

However, when I build it, I get an error:

QMClient.pas(25,73) Error: Type identifier expected
QMClient.pas(25,73) Fatal: Syntax error, ) expected but CONST found

I'm using FPC 1.0.10 dated 2003/06/26.

tnx!

g.

Ok, I made the change:
procedure QMCall(SubrName : PChar; ArgCount : shortint; const Args : array
of const); cdecl; external 'QMClient';
However, I still get the same error:
QMClient.pas(30,79) Error: Type identifier expected
QMClient.pas(30,79) Fatal: Syntax error, ) expected but CONST found

Ideas?

Thanks for the help!

g.

You have to be in delphi or objfpc mode for this to work apparently. Sorry I didn't look that up earlier.

Jonas

Yes, it's safe to ignore. It's a bug that that this warning is shown when you declare the routine as external, it's only relevant if you program the routine itself in Pascal (since then you can't use "for i := low(args) to high(args) do ...", like you can for Pascal array-of-const parameters).

Jonas

That did the trick, thanks! It does kick a warning though:

Warning: cdecl'ared functions have no high parameter

I wasn't able to find this in the documentation or the online forum. Is this directly due to the declaration and is it safe to ignore?

tnx.

g.

Ok, that's good to know. Thanks again for the fast responses!

g.