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libc11: C11 standard library

Travis CI build status Coverity Scan build status

libc11 is a public domain implementation of the C11 (ISO/IEC 9899:2011) standard library.


  • Supports the Linux, FreeBSD, OpenBSD, NetBSD, Solaris, and Mac OS X platforms.
  • Currently targets the System V ABI for x86 and x86-64, and the EABI for ARM.
  • Clean and modular design, most features can be omitted when building.
  • No build prerequisites beyond a GNU-compatible toolchain and a C99 compiler.
  • 100% free and unencumbered public domain software, usable in any context and for any purpose.

Current Status

This table summarizes which C11 features are implemented at present:

Header Spec Description Status
<assert.h> C11 7.2 Diagnostics. WIP
<complex.h> C11 7.3 Complex arithmetic.  
<ctype.h> C11 7.4 Character handling. Implemented.
<errno.h> C11 7.5 Errors. Implemented. [1]
<fenv.h> C11 7.6 Floating-point environment.  
<float.h> C11 7.7 Characteristics of floating types. Implemented.
<inttypes.h> C11 7.8 Format conversion of integer types. WIP
<iso646.h> C11 7.9 Alternative spellings. Implemented.
<limits.h> C11 7.10 Sizes of integer types. Implemented.
<locale.h> C11 7.11 Localization. Stubbed.
<math.h> C11 7.12 Mathematics. WIP
<setjmp.h> C11 7.13 Nonlocal jumps.  
<signal.h> C11 7.14 Signal handling. WIP
<stdalign.h> C11 7.15 Alignment. Implemented.
<stdarg.h> C11 7.16 Variable arguments. Implemented. [2]
<stdatomic.h> C11 7.17 Atomics. WIP
<stdbool.h> C11 7.18 Boolean type and values. Implemented.
<stddef.h> C11 7.19 Common definitions. Implemented.
<stdint.h> C11 7.20 Integer types. WIP
<stdio.h> C11 7.21 Input/output. WIP
<stdlib.h> C11 7.22 General utilities. WIP
<stdnoreturn.h> C11 7.23 _Noreturn. Implemented.
<string.h> C11 7.24 String handling. WIP
<tgmath.h> C11 7.25 Type-generic math.  
<threads.h> C11 7.26 Threads.  
<time.h> C11 7.27 Date and time.  
<uchar.h> C11 7.28 Unicode utilities.  
<wchar.h> C11 7.29 Wide character utilities. Omitted. [3]
<wctype.h> C11 7.30 Wide character utilities. Omitted. [3]


[1]Thread-local storage not supported as yet.
[2]Currently implemented only for the Clang and GCC compilers.
[3](1, 2) Legacy wide-character support purposely omitted from the library.

Platform Support

Platform Architecture Binary Interface Compilers
Bare metal any N/A Clang, GCC
Linux ARMv6+ [4] ARM EABI Clang, GCC
Linux x86 i386 SysV ABI Clang, GCC
Linux x86-64 AMD64 SysV ABI Clang, GCC
FreeBSD x86-64 AMD64 SysV ABI Clang, GCC
OpenBSD x86-64 AMD64 SysV ABI Clang, GCC
NetBSD x86-64 AMD64 SysV ABI Clang, GCC
Solaris x86-64 AMD64 SysV ABI Clang, GCC
Mac OS X x86-64 AMD64 SysV ABI Clang, GCC


[4]The armhf architecture providing a hardware floating-point unit (FPU).

See for the current build status on all supported platforms.


Installing on Unix

Configuring, building, and installing the library (by default, into /usr/local) are all performed with the standard incantations:

$ ./       # for a development checkout only
$ ./configure
$ make
$ sudo make install


Configuring a Static Build

By default on most platforms that support both, the library will be built both as a static library (libc.a) as well as a dynamic shared library ( on most Unix systems, though libc.dylib on Darwin).

If you don't require a shared library, configure the build accordingly:

$ ./configure --disable-shared

Configuring a Minimal Build

The library is thoroughly modular. Specific header files and their underlying function implementations can be omitted using the familiar ./configure --disable-FEATURE facility provided by Autoconf.

For example, if you don't require any numerics support, you might as well disable the floating-point routines and the mathematics library, as follows:

$ ./configure --disable-complex --disable-fenv --disable-float --disable-math

To review the list of features, see the output of ./configure --help.

Configuring for Bare Metal

The special none target operating system builds the library with a system-call interface where all system operations are simply no-op stubs. See the sys/syscall.h header file and the sys/posix/none/ directory for the syscall stubs that a bare-metal user of libc11 must implement.

The following example shows how one might configure a cross-compilation build on an x86-64 Linux system, targeting an x86-64 bare-metal system:

$ ./configure --build=x86_64-unknown-linux-gnu --host=x86_64-unknown-none

Provided your linker supports weak symbols, you can configure the libc11 build as per the aforementioned example, and then when linking libc11 into your kernel provide your own syscall implementations as strong symbols that override the default no-op stubs from sys/posix/none/.


Find this project at: GitHub, Bitbucket, Open Hub, SourceForge, Travis CI, Coverity Scan, Twitter, Tumblr, and COD5. See also the project's Buildbot.

Many other open-source implementations of the C standard library exist, though most of them are licensed more restrictively than this implementation:

Project License Status x86 x86-64 ARM ARM64 MIPS MIPS64 Miscellaneous
PDCLib PD/CC0 Active Yes Yes ? ? ? ? incomplete
PDPCLIB PD Active? Yes No No No No No S/3x0
Bionic BSD Active Yes Yes Yes Yes Yes Yes for Android
dietlibc GPL Active? Yes Yes Yes No Yes Yes many targets
EGLIBC LGPL Inactive Yes Yes Yes Yes Yes Yes discontinued
glibc LGPL Active Yes Yes Yes Yes Yes Yes many targets
klibc GPL/BSD Active Yes Yes Yes No Yes Yes many targets
musl MIT Active Yes Yes Yes No Yes No PPC, MicroBlaze
Newlib LGPL/BSD/etc Active Yes Yes Yes Yes Yes Yes many targets
olibc BSD Active? Yes Yes Yes Yes Yes Yes fork of Bionic
OSv MIT/BSD Active No Yes No Yes No No written in C++
uClibc LGPL Active Yes Yes Yes No Yes Yes many targets


This project is part of the DRY initiative.



If you found this software useful and would like to encourage its maintenance and further development, please consider making a $5 donation to the author(s) via Gratipay or Bitcoin.


This is free and unencumbered public domain software. For more information, see or the accompanying UNLICENSE file.


A public domain implementation of the C11 standard library.







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