Gentoo Archives: gentoo-portage-dev

From: Paul de Vrieze <pauldv@g.o>
To: gentoo-portage-dev@l.g.o
Subject: Re: [gentoo-portage-dev] DB and binary dependency
Date: Fri, 24 Mar 2006 13:20:24
In Reply to: Re: [gentoo-portage-dev] DB and binary dependency by tvali
1 On Friday 24 March 2006 12:33, tvali wrote:
2 >
3 > I meant headers as .h or .hpp files, which contain function headers.
4 > They're needed, but they are in many cases, included in pack which
5 > uses them, even if that means putting some .h's into all libs.
7 Headers are in the linux/unix world normally not included with the
8 packages that use them, but provided by the packages that the libraries
9 come from.
10 >
11 > Cant understand it. Do the *headers* change so much through versions?
12 > Is there no backward-compability in so many cases?
14 Headers only provide information to the compiler on what libraries look
15 like. Once two packages (A lib) and (B another lib that uses A) are
16 compiled, the headers are irrellevant. The only exception is if one wants
17 to compile an application/library C that depends on B. In that case it
18 needs the headers of the library provided by package B. IFF those headers
19 depend on the headers of package A, package C indirectly depends on them
20 too, and they must be available. Otherwise (if B does not "expose" A),
21 package C can compile without package A headers being present.
23 Compatibility only lives in libraries. In unix, libraries have "sonames"
24 that distinguish libraries with different interfaces. While different
25 sonames are not compatible (but can coexist), libraries with the same
26 soname are normally backward compatible. That means that you can replace
27 a library X with a library Y with the same soname and a higher version.
28 One can not necesarilly however replace it with a library Z with a lower
29 version. That would be called forward compatibility which is normally not
30 guaranteed (It may work, it may not work, or it may seem to work until
31 you put all your mission critical data in it and destroy the other
32 copies).
34 Paul
36 ps.
38 > Theory is when you know something, but it doesn't work. Practice is
39 > when something works, but you don't know why. Programmers combine
40 > theory and practice: Nothing works and they don't know why.
42 Practice without theory is when something seems to work. Until you change
43 the environment, after which things fail spectecularly.
45 --
46 Paul de Vrieze
47 Gentoo Developer
48 Mail: pauldv@g.o
49 Homepage:


Subject Author
Re: [gentoo-portage-dev] DB and binary dependency tvali <qtvali@×××××.com>