GNU C Library

Infobox Software
name = GNU C Library



caption =
developer = GNU Project
latest_release_version = 2.8
latest_release_date = release date|2008|04|11 [cite mailing list |url=http://sources.redhat.com/ml/libc-alpha/2008-04/msg00050.html |title=glibc 2.8 |date=2008-04-11 |accessdate=2008-07-19 |mailinglist=libc-alpha |last=Drepper |first=Ulrich |authorlink=Ulrich Drepper]
programming language = C
operating_system = Cross-platform
platform = Cross-platform
language =
status = Active
genre = Runtime library
source_model = Open source
license = GNU Lesser General Public License
website = http://www.gnu.org/software/libcThe GNU C Library, commonly known as glibc, is the C standard library released by the GNU Project. Originally written by the Free Software Foundation (FSF) for the GNU operating system, the library's development has been overseen by a committee since 2001, with Ulrich Drepper from Red Hat as the lead contributor and maintainer.

Released under the GNU Lesser General Public License, glibc is free software.

History

glibc was initially written mostly by Roland McGrath, working for the FSF in the 1980s.

In February 1988, FSF described glibc as having nearly completed the functionality required by ANSI C. [ cite web | url = http://www.gnu.org/bulletins/bull4.html | title = http://www.gnu.org/bulletins/bull4.html | quote = Most libraries are done. Roland McGrath [...] has a nearly complete set of ANSI C library functions. We hope they will be ready some time this spring. ] By 1992, it had the ANSI C-1989 and POSIX.1-1990 functions implemented and work was under way on POSIX.2. [ cite web | url = http://www.gnu.org/bulletins/bull12.html | title = GNU's Bulletin, vol. 1 no. 12 | quote = It now contains all of the ANSI C-1989 and POSIX.1-1990 functions, and work is in progress on POSIX.2 and Unix functions (BSD and System V) ]

A temporary fork

In the early 1990s, the developers of the Linux kernel forked glibc. Their fork, called "Linux libc", was maintained separately for years and released versions 2 through 5.

When FSF released glibc 2.0 in 1996, it had much more complete POSIX standards support, better internationalisation/multilingual support, support for IPv6, 64-bit data access, support for multithreaded applications, future version compatibility support, and the code was more portable. [ cite web | url = http://web.archive.org/web/20040411191201/http://people.redhat.com/~sopwith/old/glibc-vs-libc5.html | title = A Technical Comparison of glibc 2.x With Legacy System Libraries| author = Elliot Lee | date = 2001 ] At this point, the Linux kernel developers discontinued their fork and returned to using FSF's glibc. [ cite web | url = http://www.newsforge.com/article.pl?sid=00/10/24/0211204 | title = Forking: it could even happen to you | quote = the split between GNU LIBC and the Linux LIBC -- it went on for years while Linux stabilized, and then the forks re-merged into one project ]

The last used version of Linux libc used the internal name (soname) libc.so.5. Following on from this, glibc 2.x on Linux uses the soname libc.so.6 [ cite web | url = http://linuxmafia.com/faq/Licensing_and_Law/forking.html | title = Fear of Forking essay, see "6. glibc --> Linux libc --> glibc" ] (Alpha and IA64 architectures now use libc.so.6.1, instead). The soname is often abbreviated as libc6 (for example in the package name in debian) following the normal conventions for libraries.

According to Richard Stallman, the changes that had been made in Linux libc could not be merged back into glibc because the authorship status of that code was unclear and the GNU project is quite strict about recording copyright and authors. [ cite web | url = http://linuxmafia.com/faq/Licensing_and_Law/forking.html#foot25 | title = Fear of Forking, footnote on Stallman's merge comments ]

upported hardware and kernels

Glibc is used in systems which run many different kernels and different hardware architectures. Its most common use is in systems using the Linux kernel on x86 hardware, but officially supported hardware includes: x86, Motorola 680x0, DEC Alpha, PowerPC, ARM, ETRAX CRIS, s390, and SPARC. It officially supports the Hurd and Linux kernels, although there are heavily patched versions that run on the kernels of FreeBSD and NetBSD (from which Debian GNU/kFreeBSD and Debian GNU/NetBSD systems are built, respectively). It is also used (in an edited form) as the "libroot" of BeOS and hence Haiku.

Functionality

glibc provides the functionality required by the Single UNIX Specification, POSIX (1c, 1d, and 1j) and some of the functionality required by ISO C99, Berkeley Unix (BSD) interfaces, the System V Interface Definition (SVID) and the X/Open Portability Guide (XPG), Issue 4.2, with all extensions common to XSI (X/Open System Interface) compliant systems along with all X/Open UNIX extensions.

In addition, glibc also provides extensions which have been deemed useful or necessary while developing GNU.

Use in small devices

glibc has been criticized as being "bloated" and slower than other libraries in the past, e.g. by Linus Torvalds [Linus Torvalds: [http://ecos.sourceware.org/ml/libc-alpha/2002-01/msg00079.html Posting to the glibc mailing list] , 9 January 2002 19:02:37] and embedded Linux programmers. For this reason, several alternative C standard libraries have been created which emphasize a smaller footprint. Among them are dietlibc, uClibc, Newlib, Klibc, and EGLIBC [ [http://www.eglibc.org EGLIBC] ] .

However, many small-device projects use GNU libc over the smaller alternatives because of its application support, standards compliance, and completeness. Examples include OpenMoko [cite web
url=http://wiki.openmoko.org/wiki/OpenMoko
title=OpenMoko components
quote=We will use glibc (not uClibC) ... The alternatives may save more space and be more optimized, but are more likely to give us integration headaches|] and Familiar Linux for iPaq handhelds (when using the GPE display software). [cite web
url=http://marc.info/?l=familiar&m=118666899424374&w=2
title=Re: [Familiar] Which glibc for Familiar 0.8.4 ?
quote=Question: which version of the GLIBC was used to build the Familiar 0.8.4 ? Answer: 2.3.3|]

ee also

* Gnulib

References

External links

* [http://www.gnu.org/software/libc/ GNU libc homepage] (somewhat out-of-date)
* [http://sources.redhat.com/glibc/ GNU libc developers' page]