How to block WriteLn() in DLL?

Question

I have a DLL (from the libJasPer project). While decoding an image via jas_image_decode() in my console application the DLL shows a warning on STDOUT.

I looked in JasPer on how to disable warnings but couldn't find anything. How can I block it in Delphi/Lazarus?

Answer 1

You directly or indirectly call jas_conf_clear() which itself sets vlogmsgf to jas_vlogmsgf_stderr by default:

  jas_conf.vlogmsgf = jas_vlogmsgf_stderr;

You have to assign a different function to that variable yourself, f.e. the existing DLL function jas_vlogmsgf_discard():

  jas_conf_set_vlogmsgf( jas_vlogmsgf_discard );

...or by providing your very own function, which does its own thing when called:

type
  jas_logtype_t= Cardinal;

function jas_vlogmsgf_myown( typ: jas_logtype_t; const fmt: PAnsiChar; ap: Array of Const ): Integer; cdecl;

...whereas using Array of Const for va_list is just a wild guess by me - this could go horribly wrong. The documentation deals with this at JasPer Library > Configuration, Initialization, and Shutdown in both sections:

• Configuration, Initialization, and Shutdown and
• Logging