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

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.\"	$OpenBSD: strtoul.3,v 1.9 2002/04/30 16:31:42 mpech Exp $
.\"
.Dd June 25, 1992
.Dt STRTOUL 3
.Os
.Sh NAME
.Nm strtoul ,
.Nm strtouq
.Nd convert a string to an unsigned long or uquad_t integer
.Sh SYNOPSIS
.Fd #include <stdlib.h>
.Fd #include <limits.h>
.Ft unsigned long
.Fn strtoul "const char *nptr" "char **endptr" "int base"
.Pp
.Fd #include <sys/types.h>
.Fd #include <stdlib.h>
.Fd #include <limits.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 strtouq
function converts the string in
.Fa nptr
to a
.Li u_quad_t
value.
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.
.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
function returns the result of the conversion,
unless the value would overflow, in which case
.Dv ULONG_MAX
is returned and
.Va errno
is set to
.Er ERANGE .
If there was a leading minus sign,
.Fn strtoul
returns the (unsigned) negation of the absolute value of the number, unless
the absolute value would overflow.
In this case,
.Fn strtoul
returns
.Dv ULONG_MAX
and sets the global variable
.Va errno
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 sscanf 3 ,
.Xr strtol 3
.Sh STANDARDS
The
.Fn strtoul
function conforms to
.St -ansiC .
.Sh BUGS
Ignores the current locale.