Bob Friesenhahn wrote:
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. :-)
well... :-)
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.
OK, so they would be different because they'd have a different name; but
if I used the same release number (e.g., only the major number for
example 1, instead of 1.1) they'd still be compatible, wouldn't they? I
mean "not binary compatible" in the documentation refers only to
different names
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.
so would you suggest to use only version info and no release info, am I
right? I was only concerned about the fact that the release number of
the library is not visible anywhere and that it would force the use to
specify a name together with the number...
thanks
Lorenzo
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Lorenzo Bettini, PhD in Computer Science, DI, Univ. Torino
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