Re: [xml] wrong compiler settings for MSVC in makefile

["Igor Zlatkovic" <igor zlatkovic com>]

> I tried to link the libxml2 statically into an application, but I got
> some error messages while trying to link it. It said some symbols were
> already defined in LIBCMT.lib. The problem are different runtime library
> setting of the lib and the application I am trying to link it in. I took
> a look at the makefiles of the libxml2 and recongised it always compiled
> it with "/MD", which would be teh "Multithreaded DLL" runtime library.
> That's OK, if you compile the libxml2.dll file and the non-static
> library. But it's bad for the static lib. So I case of teh static lib it
> should be set to "/MT" (Multithreaded), if "threads" aren't set to "no"
> or "/ML" if "threads" are set to "no" in the configure.js.
> Unfortunately I don't have a diff/patch for it, because I am not quite
> sure how to handle different CFLAGS for the static and non-static lib in
> the makefile, because they used to use the same.

Things are intentionally set the way they are. It is imperative that all
libraries, have they debug symbols or not, be they static or dynamic, use
the same runtime.

When runtimes are different then:
- you do a xmlOutputBufferCreateFile(...); and your app will crash.
- you do a xmlOutputBufferCreateFd(...); and your app will crash.
- you do a xmlFreeDoc(xmlNewDoc(...)); and your app will crash.

Standard descriptors like stdin or stdout one might use in above functions
are not compatible between available runtimes. Similarily, the FILE*
returned from fopen isn't the same in all available runtimes. These pointers
and file descriptors can be used only by functions in their respective
runtimes.

Functions like xmlFree are macros which expand to free from the runtime.
But, they expand to free from your runtime, not libxml's runtime. As it
appears, malloc from one runtime is not compatible to free from another.

Another issue is compatibility between binaries produced by different
compilers, msvc and mingw for example.

To avoid all kinds of problems, I had to settle for one runtime and use it
exclusively everywhere. This implies that all applications which are based
on the binaries I produce must use the same runtime. I decided to use
msvcrt.dll and I never regretted it. Now, there are too many apps out there
to break by changing it.

First ask yourself if you really need a different runtime.
99.999999999999999% requests for another runtime come from people who want
it just because it's the default setting in Visual Studio IDE, and so they
believe it must be the right way. If your reason is different to that, then
we can add an apropriate option to configure.js and makefile.msvc to ease
the build with a different runtime.

Ciao,
Igor