2000.11.22 20:34 "Re: How to use the TIFFVGetField() interface", by Rick LaMont

I need to write a C++ program that copies verbatim a number of tags from one TIFF header to a newly created TIFF. It seems to me that I should be able to do this quite simply with the TIFFVGetField() and TIFFVSetField() subroutines.

If it were that easy, tiffcp.c would be less than 1000 lines long. My recommendation is to lift cpTag() and friends from tiffcp.c in the tools subdirectory. It's well-tested, portable code and you can call it exactly 39 times if you wish.

My understanding is that regardless of the number and type of values represented in a given tag, these can all be referenced by an va_list pointer.

What makes you think that va_list is a pointer? >:)

Seriously, va_list is an opaque type. Variables of this type may only be manipulated by va_start(), va_arg(), and va_end(). To assume anything more is prohibited by the C Standard and results in unportable programs. You may be able to jury rig something that works on some platforms by looking in stdarg.h and making a va_list variable point to a statically allocated buffer, but I would advise against it.

Rick LaMont
Dot C Software, Inc.