302 lines
6.6 KiB
HTML
302 lines
6.6 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of STRTOD</TITLE>
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</HEAD><BODY>
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<H1>STRTOD</H1>
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Section: Linux Programmer's Manual (3)<BR>Updated: 2017-09-15<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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strtod, strtof, strtold - convert ASCII string to floating-point number
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<B>#include <<A HREF="file:///usr/include/stdlib.h">stdlib.h</A>></B>
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<P>
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<B>double strtod(const char *</B><I>nptr</I><B>, char **</B><I>endptr</I><B>);</B>
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<BR>
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<B>float strtof(const char *</B><I>nptr</I><B>, char **</B><I>endptr</I><B>);</B>
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<BR>
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<B>long double strtold(const char *</B><I>nptr</I><B>, char **</B><I>endptr</I><B>);</B>
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<P>
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Feature Test Macro Requirements for glibc (see
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<B><A HREF="/cgi-bin/man/man2html?7+feature_test_macros">feature_test_macros</A></B>(7)):
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<P>
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<B>strtof</B>(),
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<B>strtold</B>():
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<DL COMPACT><DT id="1"><DD>
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_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
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</DL>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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The
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<B>strtod</B>(),
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<B>strtof</B>(),
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and
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<B>strtold</B>()
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functions convert the initial portion of the string pointed to by
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<I>nptr</I>
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to
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<I>double</I>,
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<I>float</I>,
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and
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<I>long double</I>
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representation, respectively.
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<P>
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The expected form of the (initial portion of the) string is
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optional leading white space as recognized by
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<B><A HREF="/cgi-bin/man/man2html?3+isspace">isspace</A></B>(3),
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an optional plus ('+') or minus sign ('-') and then either
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(i) a decimal number, or (ii) a hexadecimal number,
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or (iii) an infinity, or (iv) a NAN (not-a-number).
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<P>
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A
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<I>decimal number</I>
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consists of a nonempty sequence of decimal digits
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possibly containing a radix character (decimal point, locale-dependent,
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usually '.'), optionally followed by a decimal exponent.
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A decimal exponent consists of an 'E' or 'e', followed by an
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optional plus or minus sign, followed by a nonempty sequence of
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decimal digits, and indicates multiplication by a power of 10.
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<P>
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A
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<I>hexadecimal number</I>
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consists of a "0x" or "0X" followed by a nonempty sequence of
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hexadecimal digits possibly containing a radix character,
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optionally followed by a binary exponent.
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A binary exponent
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consists of a 'P' or 'p', followed by an optional
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plus or minus sign, followed by a nonempty sequence of
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decimal digits, and indicates multiplication by a power of 2.
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At least one of radix character and binary exponent must be present.
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<P>
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An
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<I>infinity</I>
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is either "INF" or "INFINITY", disregarding case.
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<P>
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A
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<I>NAN</I>
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is "NAN" (disregarding case) optionally followed by a string,
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<I>(n-char-sequence)</I>,
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where
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<I>n-char-sequence</I>
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specifies in an implementation-dependent
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way the type of NAN (see NOTES).
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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These functions return the converted value, if any.
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<P>
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If
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<I>endptr</I>
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is not NULL,
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a pointer to the character after the last character used in the conversion
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is stored in the location referenced by
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<I>endptr</I>.
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<P>
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If no conversion is performed, zero is returned and (unless
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<I>endptr</I>
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is null) the value of
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<I>nptr</I>
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is stored in the location referenced by
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<I>endptr</I>.
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<P>
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If the correct value would cause overflow, plus or minus
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<B>HUGE_VAL</B>
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(<B>HUGE_VALF</B>,
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<B>HUGE_VALL</B>)
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is returned (according to the sign of the value), and
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<B>ERANGE</B>
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is stored in
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<I>errno</I>.
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If the correct value would cause underflow, zero is
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returned and
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<B>ERANGE</B>
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is stored in
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<I>errno</I>.
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<A NAME="lbAF"> </A>
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<H2>ERRORS</H2>
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<DL COMPACT>
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<DT id="2"><B>ERANGE</B>
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<DD>
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Overflow or underflow occurred.
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</DL>
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<A NAME="lbAG"> </A>
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<H2>ATTRIBUTES</H2>
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For an explanation of the terms used in this section, see
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<B><A HREF="/cgi-bin/man/man2html?7+attributes">attributes</A></B>(7).
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<TABLE BORDER>
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<TR VALIGN=top><TD><B>Interface</B></TD><TD><B>Attribute</B></TD><TD><B>Value</B><BR></TD></TR>
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<TR VALIGN=top><TD>
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<B>strtod</B>(),
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<B>strtof</B>(),
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<B>strtold</B>()
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</TD><TD>Thread safety</TD><TD>MT-Safe locale<BR></TD></TR>
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</TABLE>
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<A NAME="lbAH"> </A>
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<H2>CONFORMING TO</H2>
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POSIX.1-2001, POSIX.1-2008, C99.
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<P>
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<B>strtod</B>()
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was also described in C89.
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<A NAME="lbAI"> </A>
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<H2>NOTES</H2>
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Since
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0 can legitimately be returned
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on both success and failure, the calling program should set
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<I>errno</I>
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to 0 before the call,
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and then determine if an error occurred by checking whether
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<I>errno</I>
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has a nonzero value after the call.
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<P>
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In the glibc implementation, the
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<I>n-char-sequence</I>
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that optionally follows "NAN"
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is interpreted as an integer number
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(with an optional '0' or '0x' prefix to select base 8 or 16)
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that is to be placed in the
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mantissa component of the returned value.
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<A NAME="lbAJ"> </A>
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<H2>EXAMPLE</H2>
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See the example on the
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<B><A HREF="/cgi-bin/man/man2html?3+strtol">strtol</A></B>(3)
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manual page;
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the use of the functions described in this manual page is similar.
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<A NAME="lbAK"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?3+atof">atof</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+atoi">atoi</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+atol">atol</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+nan">nan</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+nanf">nanf</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+nanl">nanl</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+strfromd">strfromd</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+strtol">strtol</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+strtoul">strtoul</A></B>(3)
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<A NAME="lbAL"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="3"><A HREF="#lbAB">NAME</A><DD>
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<DT id="4"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="5"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="6"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="7"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="8"><A HREF="#lbAG">ATTRIBUTES</A><DD>
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<DT id="9"><A HREF="#lbAH">CONFORMING TO</A><DD>
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<DT id="10"><A HREF="#lbAI">NOTES</A><DD>
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<DT id="11"><A HREF="#lbAJ">EXAMPLE</A><DD>
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<DT id="12"><A HREF="#lbAK">SEE ALSO</A><DD>
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<DT id="13"><A HREF="#lbAL">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:58 GMT, March 31, 2021
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</BODY>
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</HTML>
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