NetBSD/lib/libc/stdlib/strtoul.3

.\"	$NetBSD: strtoul.3,v 1.17 2003/04/16 13:34:47 wiz Exp $
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.\"     from: @(#)strtoul.3	8.1 (Berkeley) 6/4/93
.\"
.Dd August 11, 2002
.Dt STRTOUL 3
.Os
.Sh NAME
.Nm strtoul ,
.Nm strtoull ,
.Nm strtoumax ,
.Nm strtouq
.Nd "convert a string to an unsigned long, unsigned long long, uintmax_t or uquad_t integer"
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdlib.h
.In limits.h
.Ft unsigned long int
.Fn strtoul "const char * restrict nptr" "char ** restrict endptr" "int base"
.Ft unsigned long long int
.Fn strtoull "const char * restrict nptr" "char ** restrict endptr" "int base"
.Pp
.In inttypes.h
.Ft uintmax_t
.Fn strtoumax "const char * restrict nptr" "char ** restrict endptr" "int base"
.Pp
.In sys/types.h
.In stdlib.h
.In limits.h
.Ft u_quad_t
.Fn strtouq "const char * restrict nptr" "char ** restrict endptr" "int base"
.Sh DESCRIPTION
The
.Fn strtoul
function
converts the string in
.Fa nptr
to an
.Em unsigned long int
value.
The
.Fn strtoull
function
converts the string in
.Fa nptr
to an
.Em unsigned long long int
value.
The
.Fn strtoumax
function
converts the string in
.Fa nptr
to an
.Em uintmax_t
value.
The
.Fn strtouq
function
converts the string in
.Fa nptr
to a
.Em u_quad_t
value.
The conversion is done according to the given
.Fa base ,
which must be between 2 and 36 inclusive,
or be the special value 0.
.Pp
The string may begin with an arbitrary amount of white space
(as determined by
.Xr isspace 3 )
followed by a single optional
.Ql +
or
.Ql -
sign.
If
.Fa base
is zero or 16,
the string may then include a
.Ql 0x
prefix,
and the number will be read in base 16; otherwise, a zero
.Fa base
is taken as 10 (decimal) unless the next character is
.Ql 0 ,
in which case it is taken as 8 (octal).
.Pp
The remainder of the string is converted to an
.Em unsigned long
value in the obvious manner,
stopping at the end of the string
or at the first character that does not produce a valid digit
in the given base.
(In bases above 10, the letter
.Ql A
in either upper or lower case
represents 10,
.Ql B
represents 11, and so forth, with
.Ql Z
representing 35.)
.Pp
If
.Fa endptr
is non nil,
.Fn strtoul
stores the address of the first invalid character in
.Fa *endptr .
If there were no digits at all, however,
.Fn strtoul
stores the original value of
.Fa nptr
in
.Fa *endptr .
(Thus, if
.Fa *nptr
is not
.Ql \e0
but
.Fa **endptr
is
.Ql \e0
on return, the entire string was valid.)
.Sh RETURN VALUES
The
.Fn strtoul
function
returns either the result of the conversion
or, if there was a leading minus sign,
the negation of the result of the conversion,
unless the original (non-negated) value would overflow;
in the latter case,
.Fn strtoul
returns
.Dv ULONG_MAX ,
.Fn strtoull
returns
.Dv ULLONG_MAX ,
.Fn strtoumax
returns
.Dv UINTMAX_MAX ,
and the global variable
.Va errno
is set to
.Er ERANGE .
.Pp
There is no way to determine if
.Fn strtoul
has processed a negative number (and returned an unsigned value) short of
examining the string in
.Fa nptr
directly.
.Sh EXAMPLES
Ensuring that a string is a valid number (i.e., in range and containing no
trailing characters) requires clearing
.Va errno
beforehand explicitly since
.Va errno
is not changed on a successful call to
.Fn strtoul ,
and the return value of
.Fn strtoul
cannot be used unambiguously to signal an error:
.Bd -literal -offset indent
char *ep;
unsigned long ulval;

\&...

errno = 0;
ulval = strtoul(buf, &ep, 10);
if (buf[0] == '\e0' || *ep != '\e0')
	goto not_a_number;
if (errno == ERANGE && ulval == ULONG_MAX)
	goto out_of_range;
.Ed
.Pp
This example will accept
.Dq 12
but not
.Dq 12foo
or
.Dq 12\en .
If trailing whitespace is acceptable, further checks must be done on
.Va *ep ;
alternately, use
.Xr sscanf 3 .
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er ERANGE
The given string was out of range; the value converted has been clamped.
.El
.Sh SEE ALSO
.Xr strtoimax 3 ,
.Xr strtol 3 ,
.Xr strtoll 3
.Sh STANDARDS
The
.Fn strtoul
function
conforms to
.St -ansiC .
The
.Fn strtoull
and
.Fn strtoumax
functions conform to
.St -isoC99 .
.Sh BUGS
Ignores the current locale.