This document serves as an overview of HelenOS standard user space API implemented in ''HelenOS C library'' and the relation of this API to common standards such as "C Standard Library" (as defined by various ISO C standards, such as C99) and ''C POSIX Library'' standards.

'''General note:''' The primary aim of ''HelenOS C library'' is not a to be 100% compatible with the standards. For both many fundamental reasons (HelenOS is not an unix-like operating system) and practical reasons (our subjective dislike of some aspects of the standards, security issues, etc.) the ''HelenOS C library'' follows the standards very loosely. Many functions are not implemented because lack of current need or simple because lack of manpower and many functions closely resemble their standard-compliant counterparts, but behave very slightly differently.

== unistd.h ==

Implemented functions (items marked wit D have been removed in the development version):

|| '''Function''' || '''Based on'''         || '''Std Compliant''' || '''Note'''                                          ||
|| chdir (D)      || POSIX-1-2001           || mostly              ||                                                     ||
|| close (D)      || POSIX-1.2001           || mostly              ||                                                     ||
|| dup2 (D)       || POSIX-1.2001           || mostly              ||                                                     ||
|| exit           || POSIX-1.2001, C89, C99 || mostly              || should be defined in stdlib.h by POSIX              ||
|| fsync (D)      || POSIX.1-2001           || partially           || non-standard semantics                              ||
|| ftruncate (D)  || POSIX.1-2001           || partially           || the absolute offset is aoff64_t                     ||
|| getcwd (D)     || POSIX.1-2001           || mostly              ||                                                     ||
|| lseek (D)      || POSIX.1-2001           || partially           || relative offset is off64_t                          ||
|| read (D)       || POSIX.1-2001           || mostly              ||                                                     ||
|| rmdir (D)      || POSIX.1-2001           || mostly              ||                                                     ||
|| sleep          || POSIX.1-2001           || mostly              ||                                                     ||
|| unlink (D)     || POSIX.1-2001           || mostly              ||                                                     ||
|| usleep         || POSIX.1-2001           || mostly              || obsoleted and replaced by nanosleep in POSIX.1-2008 ||
|| write (D)      || POSIX.1-2001           || mostly              ||                                                     ||

Unimplemented functions:

TBD