path: root/lib/libc/stdlib/strtoul.3

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.\"	$OpenBSD: strtoul.3,v 1.22 2013/08/14 06:32:28 jmc Exp $
.\"
.Dd $Mdocdate: August 14 2013 $
.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 or uintmax_t integer
.Sh SYNOPSIS
.In limits.h
.In stdlib.h
.Ft unsigned long
.Fn strtoul "const char *nptr" "char **endptr" "int base"
.Ft unsigned long long
.Fn strtoull "const char *nptr" "char **endptr" "int base"
.In inttypes.h
.Ft uintmax_t
.Fn strtoumax "const char *nptr" "char **endptr" "int base"
.In sys/types.h
.In limits.h
.In stdlib.h
.Ft u_quad_t
.Fn strtouq "const char *nptr" "char **endptr" "int base"
.Sh DESCRIPTION
The
.Fn strtoul
function converts the string in
.Fa nptr
to an
.Li unsigned long
value.
The
.Fn strtoull
function converts the string in
.Fa nptr
to an
.Li unsigned long long
value.
The
.Fn strtoumax
function converts the string in
.Fa nptr
to a
.Li umaxint_t
value.
The
.Fn strtouq
function is a deprecated equivalent of
.Fn strtoull
and is provided for backwards compatibility with legacy programs.
The conversion is done according to the given
.Fa base ,
which must be a number between 2 and 36 inclusive
or the special value 0.
If the string in
.Fa nptr
represents a negative number, it will be converted to its unsigned equivalent.
This behavior is consistent with what happens when a signed integer type is
cast to its unsigned counterpart.
.Pp
The string may begin with an arbitrary amount of whitespace
(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
.Li 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-null,
.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 ,
.Fn strtoull ,
.Fn strtoumax
and
.Fn strtouq
functions return 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.
If overflow occurs,
.Fn strtoul
returns
.Dv ULONG_MAX ,
.Fn strtoull
returns
.Dv ULLONG_MAX ,
.Fn strtoumax
returns
.Dv UINTMAX_MAX ,
.Fn strtouq
returns
.Dv ULLONG_MAX
and the global variable
.Va errno
is set to
.Er ERANGE .
If no conversion could be performed, 0 is returned;
the global variable
.Va errno
is also set to
.Er EINVAL ,
though this is not portable across all platforms.
.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 sscanf 3 ,
.Xr strtol 3
.Sh STANDARDS
The
.Fn strtoul ,
.Fn strtoull ,
and
.Fn strtoumax
functions conform to
.St -ansiC-99 .
The
.Fn strtouq
function is a
.Bx
extension and is provided for backwards compatibility with legacy programs.
.Sh BUGS
Ignores the current locale.