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<!-- Copyright (C) 2003 Red Hat, Inc.                                -->
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>C and math library overview</TITLE
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>eCos Reference Manual</TH
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><DIV
CLASS="CHAPTER"
><H1
><A
NAME="C-AND-MATH-LIBRARY-OVERVIEW">Chapter 13. C and math library overview</H1
><DIV
CLASS="TOC"
><DL
><DT
><B
>Table of Contents</B
></DT
><DT
><A
HREF="c-and-math-library-overview.html#INCLUDE-NON-ISO-FUNCTIONS"
>Included non-ISO functions</A
></DT
><DT
><A
HREF="math-library-compatibility-modes.html"
>Math library compatibility modes</A
></DT
><DT
><A
HREF="libc-implementation-details.html"
>Some implementation details</A
></DT
><DT
><A
HREF="libc-thread-safety.html"
>Thread safety</A
></DT
><DT
><A
HREF="c-library-startup.html"
>C library startup</A
></DT
></DL
></DIV
><A
NAME="ISO-C-AND-MATH-LIBRARIES"
></A
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>eCos</I
></SPAN
> provides compatibility with the
	ISO 9899:1990 specification for the standard C library, which
	is essentially the same as the better-known ANSI C3.159-1989
	specification (C-89).</P
><P
>There are three aspects of this compatibility supplied by <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>eCos</I
></SPAN
>.
First there is a <I
CLASS="FIRSTTERM"
>C library</I
> which
implements the functions defined by the ISO standard, except for the
mathematical functions. This is provided by the eCos C library
packages. </P
><P
>Then <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>eCos</I
></SPAN
> provides a math
library, which implements the mathematical functions from the ISO
C library. This distinction between C and math libraries is frequently
drawn &#8212; most standard C library implementations provide
separate linkable files for the two, and the math library contains
all the functions from the <TT
CLASS="FILENAME"
>math.h</TT
> header
file.</P
><P
>There is a third element to the ISO C library, which is the
environment in which applications run when they use the standard
C library. This environment is set up by the C library startup procedure
(<A
HREF="c-library-startup.html"
>the Section called <I
>C library startup</I
></A
>)
and it provides (among other things) a <TT
CLASS="FUNCTION"
>main()</TT
> entry
point function, an <TT
CLASS="FUNCTION"
>exit()</TT
> function that
does the cleanup required by the standard (including handlers registered
using the <TT
CLASS="FUNCTION"
>atexit()</TT
> function), and an environment
that can be read with <TT
CLASS="FUNCTION"
>getenv()</TT
>. </P
><P
>The description in this manual focuses on the <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>eCos</I
></SPAN
>-specific
aspects of the C library (mostly related to <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>eCos</I
></SPAN
>'s
configurability) as well as mentioning the omissions from the standard
in this release. We do not attempt to define the semantics of each
function, since that information can be found in the ISO, ANSI,
POSIX and IEEE standards, and the many good books that have been
written about the standard C library, that cover usage of these
functions in a more general and useful way.</P
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="INCLUDE-NON-ISO-FUNCTIONS">Included non-ISO functions</H1
><P
>The following functions from the POSIX specification
are included for convenience: </P
><P
>	<TT
CLASS="LITERAL"
>extern char **</TT
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>environ</I
></SPAN
> variable
(for setting up the environment for use with <TT
CLASS="FUNCTION"
>getenv()</TT
>)</P
><P
>	<TT
CLASS="FUNCTION"
>_exit()</TT
> </P
><P
>	<TT
CLASS="FUNCTION"
>strtok_r()</TT
> </P
><P
>	<TT
CLASS="FUNCTION"
>rand_r()</TT
> </P
><P
>	<TT
CLASS="FUNCTION"
>asctime_r()</TT
> </P
><P
>	<TT
CLASS="FUNCTION"
>ctime_r()</TT
> </P
><P
>	<TT
CLASS="FUNCTION"
>localtime_r()</TT
> </P
><P
>	<TT
CLASS="FUNCTION"
>gmtime_r()</TT
> </P
><P
><SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>eCos</I
></SPAN
> provides the following additional
implementation-specific functions within the standard C library
to adjust the date and time settings:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>void <TT
CLASS="FUNCTION"
>cyg_libc_time_setdst</TT
>( 
  cyg_libc_time_dst state
);</PRE
></TD
></TR
></TABLE
><P
>This function sets the state of Daylight Savings Time. The
values for state are:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>CYG_LIBC_TIME_DSTNA   unknown
CYG_LIBC_TIME_DSTOFF  off
CYG_LIBC_TIME_DSTON   on</PRE
></TD
></TR
></TABLE
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>void <TT
CLASS="FUNCTION"
>cyg_libc_time_setzoneoffsets</TT
>( 
  time_t stdoffset, time_t dstoffset
);</PRE
></TD
></TR
></TABLE
><P
>This function sets the offsets from UTC used when Daylight
Savings Time is enabled or disabled. The offsets are in time_t&#8217;s,
which are seconds in the current inplementation.</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
><TT
CLASS="FUNCTION"
>Cyg_libc_time_dst cyg_libc_time_getzoneoffsets</TT
>( 
  time_t *stdoffset, time_t *dstoffset
);</PRE
></TD
></TR
></TABLE
><P
>This function retrieves the current setting for Daylight Savings
Time along with the offsets used for both STD and DST. The offsets
are both in time_t&#8217;s, which are seconds in the
current implementation.</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
><TT
CLASS="FUNCTION"
>cyg_bool cyg_libc_time_settime</TT
>( 
  time_t utctime
);</PRE
></TD
></TR
></TABLE
><P
>This function sets the current time for the system The time
is specified as a <SPAN
CLASS="TYPE"
>time_t</SPAN
> in UTC.
It returns non-zero on error.</P
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