x15/doc/cenv.9.txt

CENV(9)
========
:doctype:       manpage
:man source:    X15
:man manual:    X15 C environment

NAME
----

cenv - C environment

DESCRIPTION
-----------

This document describes the C environment of the kernel, including
available standard headers and interfaces.

Standard
~~~~~~~~

X15 must be built with a C compiler supporting the ISO/IEC 9899:2011
(C11) specification with some GCC extensions. It can currently be built
with the GCC and Clang compilers.

Environment
~~~~~~~~~~~

The kernel uses the freestanding execution environment. This means the
compiler is expected to provide the following headers :

** cheader:float
** cheader:iso646
** cheader:limits
** cheader:stdalign
** cheader:stdarg
** cheader:stdbool
** cheader:stddef
** cheader:stdint
** cheader:stdnoreturn

X15 augments the environment with a small subset of the functions provided
in hosted environments. The additional headers are :

** cheader:assert
** cheader:errno
** cheader:limits
** cheader:stdio
** cheader:string

Note that these headers do not provide the complete set of interfaces
expected in a hosted environment.

Formatting functions
~~~~~~~~~~~~~~~~~~~~

Of particular interest is the cheader:stdio header which provides a subset
of the printf and scanf family of functions.

The supported functions are :

** cfunction:getchar
** cfunction:putchar
** cfunction:sprintf
** cfunction:snprintf
** cfunction:vsprintf
** cfunction:vsnprintf
** cfunction:sscanf
** cfunction:vsscanf

The *EOF* macro is also provided.

The formatting functions only implement a subset of what the standard
defines, namely :

** cfunction:sprintf :
*** flags: # 0 - ' ' (space) +
*** field width is supported
*** precision is supported
** cfunction:sscanf :
*** flags: *
*** field width is supported
** common to both :
*** modifiers: hh h l ll z t
*** specifiers: d i o u x X c s p n %

Floating point conversions are currently not supported, but this may change
in the future.

SEE
---

manpage:intro

{x15-operating-system}