244 lines
5.9 KiB
Groff
244 lines
5.9 KiB
Groff
.\" $NetBSD: strtod.3,v 1.29 2016/11/07 21:52:36 riastradh Exp $
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.\"
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.\" Copyright (c) 1990, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" the American National Standards Committee X3, on Information
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.\" Processing Systems.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" from: @(#)strtod.3 8.1 (Berkeley) 6/4/93
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.\"
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.Dd November 4, 2016
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.Dt STRTOD 3
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.Os
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.Sh NAME
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.Nm strtod ,
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.Nm strtof ,
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.Nm strtold
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.Nd convert
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.Tn ASCII
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string to double, float, or long double
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In stdlib.h
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.Ft double
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.Fn strtod "const char * restrict nptr" "char ** restrict endptr"
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.Ft float
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.Fn strtof "const char * restrict nptr" "char ** restrict endptr"
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.Ft long double
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.Fn strtold "const char * restrict nptr" "char ** restrict endptr"
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.Sh DESCRIPTION
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The
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.Fn strtod
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function converts the initial portion of the string
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pointed to by
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.Fa nptr
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to
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.Em double
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representation.
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.Pp
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The
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.Fn strtof
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function converts the initial portion of the string
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pointed to by
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.Fa nptr
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to
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.Em float
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representation.
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.Pp
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The
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.Fn strtold
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function converts the initial portion of the string
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pointed to by
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.Fa nptr
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to
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.Em long double
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representation.
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.Pp
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The expected form of the string is an optional plus
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.Pq Sq +
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or minus sign
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.Pq Sq \-
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followed by one of the following:
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.Bl -dash
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.It
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a sequence of digits optionally containing
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a decimal-point character, optionally followed by an exponent.
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An exponent consists of an
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.Sq E
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or
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.Sq e ,
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followed by an optional plus
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or minus sign, followed by a sequence of digits.
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.It
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one of
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.Li INF
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or
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.Li INFINITY ,
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ignoring case.
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.It
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one of
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.Li NAN
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or
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.Li NAN(n-char-sequence-opt) ,
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ignoring case.
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This implementation currently does not interpret such a sequence.
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.El
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.Pp
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Leading white-space characters in the string (as defined by the
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.Xr isspace 3
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function) are skipped.
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.Sh RETURN VALUES
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The
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.Fn strtod ,
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.Fn strtof ,
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and
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.Fn strtold
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functions return the converted value, if any.
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.Pp
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A character sequence
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.Li INF
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or
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.Li INFINITY
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is converted to \*(If,
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if supported, else to the largest finite floating-point number representable
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on the machine (i.e.,
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.Tn VAX ) .
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.Pp
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A character sequence
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.Li NAN
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or
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.Li NAN(n-char-sequence-opt)
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is converted to a quiet \*(Na, if supported, else remains unrecognized (i.e.,
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.Tn VAX ) .
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.Pp
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If
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.Fa endptr
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is not
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.Dv NULL ,
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a pointer to the character after the last character used
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in the conversion is stored in the location referenced by
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.Fa endptr .
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.Pp
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If no conversion is performed, zero is returned and the value of
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.Fa nptr
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is stored in the location referenced by
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.Fa endptr .
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.Pp
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If the correct value is too large in magnitude to be represented
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.Pq Sq overflow ,
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plus or minus
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.Dv HUGE_VAL ,
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.Dv HUGE_VALF ,
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or
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.Dv HUGE_VALL
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is returned (according to the return type and sign of the value), and
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.Dv ERANGE
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is stored in
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.Va errno .
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.Pp
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If the correct value is too small in magnitude to be represented
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normally with full precision
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.Pq Sq underflow ,
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the closest subnormal value, or zero, is returned, and
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.Dv ERANGE
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is stored in
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.Va errno .
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.Sh EXAMPLES
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Since there is no out-of-band channel or sentinel value to indicate an
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error, callers who wish to know whether there was overflow or underflow
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must set
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.Va errno
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to zero before calling
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.Fn strtod ,
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.Fn strtof ,
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or
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.Fn strtold ;
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in the case of no underflow or overflow, these functions preserve
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.Va errno .
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.Pp
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To check for syntax errors, callers must
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.Em also
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check whether
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.Fa endptr
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was updated to reflect the true end of the string in order to determine
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whether the full string was consumed or whether there were additional
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erroneous characters in it.
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.Bd -literal -offset abcd
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char *end;
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double d;
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\&...
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errno = 0;
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d = strtod(s, &end);
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if (end == s)
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errx(EXIT_FAILURE, "invalid syntax");
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if (end[0] != '\e0')
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errx(EXIT_FAILURE, "trailing garbage");
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if (errno) {
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assert(errno == ERANGE);
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assert(isinf(d) || d == 0 ||
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fpclassify(d) == FP_SUBNORMAL);
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warnx("%s", isinf(d) ? "overflow" : "underflow");
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}
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/* d is the best floating-point approximation to the number in s */
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.Ed
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.Sh ERRORS
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.Bl -tag -width Er
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.It Bq Er ERANGE
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The conversion resulted in floating-point underflow or overflow.
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.El
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.Sh SEE ALSO
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.Xr atof 3 ,
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.Xr atoi 3 ,
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.Xr atol 3 ,
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.Xr math 3 ,
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.Xr strtol 3 ,
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.Xr strtoul 3
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.Sh STANDARDS
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The
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.Fn strtod
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function
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conforms to
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.St -ansiC .
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The
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.Fn strtof
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and
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.Fn strtold
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functions conform to
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.St -isoC-99 .
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.Sh HISTORY
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The
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.Fn strtof
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and
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.Fn strtold
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functions appeared in
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.Nx 4.0 .
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