Re: version and release number

[Bob Friesenhahn]

On Thu, 16 Apr 2009, Lorenzo Bettini wrote:

> Never try to set the interface numbers so that they correspond to the release 
> number of your package. This is an abuse that only fosters misunderstanding 
> of the purpose of library versions. Instead, use the -release flag (see 
> Release numbers), but be warned that every release of your package will not 
> be binary compatible with any other release.
>
> what I don't understand is the "not binary compatible": if I use, say 1.0 for 
> the release flag (and the version number correctly as stated in the manual), 
> and release another implementation of the library with the incremented 
> version number but with the same release number, why won't it be binary 
> compatible?
>
> Or does "not binary compatible" apply only if I increment also the release 
> number?

I sense some confusion. :-)

The -release option specifies part of the base naming for your library 
so that it becomes part of the base library name.  For example, 
libfoo-1.0.so and libfoo-2.0.so.  To the operating system these 
libraries are completely different and might have well been named 
libfoo.so and libbar.so.  The libraries might otherwise be entirely 
the same and could be "binary compatible" but the operating system 
won't know it.  Very few packages use the -release option.

The -version-info option specifies library versioning information that 
the operating system will use when deciding which similarly named 
library to use.  On most Unix systems, this forms the numeric part in 
the library file name after ".so".  Different systems use different 
rules when deciding how to treat this version information.  Assuming 
that libraries are from the same release, the correct library will be 
used as long as you follow the libtool rules when updating the 
-version-info argument.

There are many forms of "binary compatible".  For example, a newer 
library might add a new function but otherwise be the same so an 
already existing application (using an older library) can safely use 
it.  A newer application depending on the newer library could not 
safely use the older library since it might be using the new function 
the new function might not be present.

Bob
--
Bob Friesenhahn
address@hidden, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/