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

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.\"     from: @(#)strtoul.3	8.1 (Berkeley) 6/4/93
.\"
.Dd April 30, 2015
.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
.Ft unsigned long int
value.
The
.Fn strtoull
function
converts the string in
.Fa nptr
to an
.Ft unsigned long long int
value.
The
.Fn strtoumax
function
converts the string in
.Fa nptr
to an
.Ft uintmax_t
value.
The
.Fn strtouq
function
converts the string in
.Fa nptr
to a
.Ft u_quad_t
value.
.Pp
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 appropriate
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, the functions store the address of the first invalid character in
.Fa *endptr .
If there were no digits at all, however,
the functions store 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 ,
.Fn strtouq
returns
.Dv UQUAD_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.
If the
.Fa base
argument is not supported then
.Va errno
is set to
.Er EINVAL
and the functions return 0.
.Pp
If no error occurs,
.Va errno
is left unchanged.
This behavior (which is unlike most library functions) is guaranteed
by the pertinent standards.
.Sh EXAMPLES
Because the return value of
.Fn strtoul
cannot be used unambiguously to detect an error,
.Va errno
is left unchanged after a successful call.
To ensure that a string is a valid number (i.e., in range and containing no
trailing characters), clear
.Va errno
beforehand explicitly, then check it afterwards:
.Bd -literal -offset indent
char *ep;
unsigned long ulval;

\&...

errno = 0;
ulval = strtoul(buf, \*[Am]ep, 10);
if (buf[0] == '\e0' || *ep != '\e0')
	goto not_a_number;
if (errno == ERANGE \*[Am]\*[Am] 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 EINVAL
The
.Ar base
is not between 2 and 36 and does not contain the special value 0.
.It Bq Er ERANGE
The given string was out of range; the value converted has been clamped.
.El
.Sh SEE ALSO
.Xr atof 3 ,
.Xr atoi 3 ,
.Xr atol 3 ,
.Xr atoll 3 ,
.Xr strtod 3 ,
.Xr strtoi 3 ,
.Xr strtoimax 3 ,
.Xr strtol 3 ,
.Xr strtoll 3 ,
.Xr strtou 3
.Sh STANDARDS
The
.Fn strtoul
function
conforms to
.St -ansiC .
The
.Fn strtoull
and
.Fn strtoumax
functions conform to
.St -isoC-99 .
.Pp
The
.Fn strtouq
function is a
.Bx
legacy function equivalent to
.Fn strtoull
and should not be used in a new code.
.Sh BUGS
Ignores the current locale.