Hello,
We ran into an issue when using OpenImageIO 2.1.9.0 (built and installed
on windows with vcpkg) and our own version of fmt 5.3.0
(https://github.com/fmtlib/fmt) that we use within our project.
Including both <fmt/format.h> and <OpenImageIO/imagecache.h> (possibly
the same issue with other headers) will result in the following
compilation errors (sorry, the output is in french, but a rough summary
is provided below):
OpenImageIO/strutil.h(44,1): warning C4005: 'FMT_USE_GRISU' :
redéfinition de macro (compilation du fichier source
src\ui\renderoutputview.cpp)
ext\fmt-5.3.0\include\fmt\format.h(165): message : voir la définition
précédente de 'FMT_USE_GRISU' (compilation du fichier source
src\ui\renderoutputview.cpp)
OpenImageIO\fmt/ostream.h(22,9): error C2059: erreur de syntaxe : '<'
(compilation du fichier source src\ui\renderoutputview.cpp)
OpenImageIO\fmt/ostream.h(22,1): error C2238: jetons inattendus avant
';' (compilation du fichier source src\ui\renderoutputview.cpp)
OpenImageIO\fmt/ostream.h(25,19): error C2143: erreur de syntaxe :
absence de ')' avant '<' (compilation du fichier source
src\ui\renderoutputview.cpp)
OpenImageIO\fmt/ostream.h(25,19): error C2143: erreur de syntaxe :
absence de ';' avant '<' (compilation du fichier source
src\ui\renderoutputview.cpp)
OpenImageIO\fmt/ostream.h(25,1): error C2059: erreur de syntaxe : '<'
(compilation du fichier source src\ui\renderoutputview.cpp)
OpenImageIO\fmt/ostream.h(25,1): error C2059: erreur de syntaxe : ')'
(compilation du fichier source src\ui\renderoutputview.cpp)
OpenImageIO\fmt/ostream.h(25,1): error C2334: jetons inattendus avant
':' ; corps apparent de la fonction ignoré (compilation du fichier
source src\ui\renderoutputview.cpp)
... which basically warns about a macro redefinition (FMT_USE_GRISU) and
a bunch of syntax errors in OpenImageIO\fmt/ostream.h. The problem is
that in this compilation unit, our own copy of fmt/format.h is included
first (at version 5.3.0) and conflicts with the version bundled by
OpenImageIO (in this case, OpenImageIO/fmt/ostream.h includes
OpenImageIO/fmt/format.h, but the header guard FMT_FORMAT_H_ has already
been set by our own copy which is at an incompatible version).
A simple workaround would be to match the two versions of fmt, or maybe
to set OIIO_USE_FMT=0. However, my question was if fmt was supposed to
be exposed in the public API of OpenImageIO in the first place, or if it
is just an implementation detail that should not be visible. In the
former case, we would need to ensure that either a single version of fmt
is used by both OpenImageIO and our project, or that both versions are
the same (which unfortunately is not that easy when pulling the package
from an external source like vcpkg).
In any case, I'm not sure this is an issue of OpenImageIO per se, but
rather a general issue of dependency management in C++. Might there be a
way to somehow avoid such conflicts in the future? Possibly by not
exposing the fmt headers in the public headers of OIIO, or, if not
possible (because of e.g. templates) rename the "fmt::" namespace of the
copy of fmt used by OIIO to something like "oiio_fmt::"? (this would not
fix the header guard issue though).
Regards,
Alexandre Bléron
artineering.io
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