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[thirdparty/man-pages.git] / man3 / strtod.3

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.\"     @(#)strtod.3	5.3 (Berkeley) 6/29/91
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.\" Modified Sun Aug 21 17:16:22 1994 by Rik Faith (faith@cs.unc.edu)
.\" Modified Sat May 04 19:34:31 MET DST 1996 by Michael Haardt
.\"   (michael@cantor.informatik.rwth-aachen.de)
.\" Added strof, strold, aeb, 2001-06-07
.\"
.TH STRTOD 3 2001-06-07 "Linux" "Library functions"
.SH NAME
strtod, strtof, strtold \- convert ASCII string to floating point number
.SH SYNOPSIS
.B #include <stdlib.h>
.sp
.BI "double strtod(const char *" nptr ", char **" endptr );
.sp
.BR "#define _XOPEN_SOURCE=600" "   /* or #define _ISOC99_SOURCE */"
.br
.B #include <stdlib.h>
.sp
.BI "float strtof(const char *" nptr ", char **" endptr );
.br
.BI "long double strtold(const char *" nptr ", char **" endptr );
.SH DESCRIPTION
The
.BR strtod (),
.BR strtof (),
and
.BR strtold ()
functions convert the initial portion of the string pointed to by
.I nptr
to
.IR double ,
.IR float ,
and
.I long double 
representation, respectively.

The expected form of the (initial portion of the) string is
optional leading white space as recognized by \fIisspace\fP(3),
an optional plus (``+'') or minus sign (``\-'') and then either
(i) a decimal number, or (ii) a hexadecimal number,
or (iii) an infinity, or (iv) a NAN (not-a-number).
.LP
A
.I "decimal number"
consists of a nonempty sequence of decimal digits
possibly containing a radix character (decimal point, locale dependent,
usually ``.''), optionally followed by a decimal exponent.  A
decimal exponent consists of an ``E'' or ``e'', followed by an
optional plus or minus sign, followed by a non-empty sequence of
decimal digits, and indicates multiplication by a power of 10.
.LP
A
.I "hexadecimal number"
consists of a ``0x'' or ``0X'' followed by a nonempty sequence of
hexadecimal digits possibly containing a radix character,
optionally followed by a binary exponent. A binary exponent
consists of a ``P'' or ``p'', followed by an optional
plus or minus sign, followed by a non-empty sequence of
decimal digits, and indicates multiplication by a power of 2.
At least one of radix character and binary exponent must be present.
.LP
An
.I infinity
is either ``INF'' or ``INFINITY'', disregarding case.
.LP
A
.I NAN
is ``NAN'' (disregarding case) optionally followed by `(',
a sequence of characters, followed by ')'.
The character string specifies in an implementation-dependent
way the type of NAN.

.SH "RETURN VALUE"
These functions return the converted value, if any.

If
.I endptr
is not NULL,
a pointer to the character after the last character used in the conversion
is stored in the location referenced by
.IR endptr .

If no conversion is performed, zero is returned and the value of
.I nptr
is stored in the location referenced by
.IR endptr .

If the correct value would cause overflow, plus or minus
.B HUGE_VAL
.RB ( HUGE_VALF ,
.BR HUGE_VALL )
is returned (according to the sign of the value), and
.B ERANGE
is stored in
.IR errno .
If the correct value would cause underflow, zero is
returned and
.B ERANGE
is stored in 
.IR errno .
.SH ERRORS
.TP
.B ERANGE
Overflow or underflow occurred.
.SH "CONFORMING TO"
ANSI C describes
.BR strtod (),
C99
describes the other two functions.
.SH NOTES
Since 
0 can legitimately be returned 
on both success and failure, the calling program should set
.I errno
to 0 before the call, 
and then determine if an error occurred by checking whether
.I errno
has a non-zero value after the call.
.SH EXAMPLE
See the example on the
.BR strtol (3)
manual page; 
the use of the functions described in this manual page is similar.
.SH "SEE ALSO"
.BR atof (3),
.BR atoi (3),
.BR atol (3),
.BR strtol (3),
.BR strtoul (3)