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

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.\"	$OpenBSD: strtol.3,v 1.27 2015/04/14 22:16:03 nicm Exp $
.\"
.Dd $Mdocdate: April 14 2015 $
.Dt STRTOL 3
.Os
.Sh NAME
.Nm strtol ,
.Nm strtoll ,
.Nm strtoimax ,
.Nm strtoq
.Nd convert string value to a long, long long or intmax_t integer
.Sh SYNOPSIS
.In limits.h
.In stdlib.h
.Ft long
.Fn strtol "const char *nptr" "char **endptr" "int base"
.Ft long long
.Fn strtoll "const char *nptr" "char **endptr" "int base"
.In inttypes.h
.Ft intmax_t
.Fn strtoimax "const char *nptr" "char **endptr" "int base"
.In sys/types.h
.In limits.h
.In stdlib.h
.Ft quad_t
.Fn strtoq "const char *nptr" "char **endptr" "int base"
.Sh DESCRIPTION
The
.Fn strtol
function converts the string in
.Fa nptr
to a
.Vt long
value.
The
.Fn strtoll
function converts the string in
.Fa nptr
to a
.Vt long long
value.
The
.Fn strtoimax
function converts the string in
.Fa nptr
to an
.Vt intmax_t
value.
The
.Fn strtoq
function is a deprecated equivalent of
.Fn strtoll
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.
.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 a
.Vt long ,
.Vt long long ,
or
.Vt intmax_t
value in the obvious manner,
stopping at the first character which is not 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 strtol
stores the address of the first invalid character in
.Fa *endptr .
If there were no digits at all, however,
.Fn strtol
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 strtol ,
.Fn strtoll ,
.Fn strtoimax ,
and
.Fn strtoq
functions return the result of the conversion.
If overflow or underflow occurs,
.Va errno
is set to
.Er ERANGE
and the function return value is as follows:
.Bl -column "strtoimaxXX" "INTMAX_MIN" "INTMAX_MAX" -offset indent
.It Sy Function Ta Sy underflow Ta Sy overflow
.It Fn strtol Ta Dv LONG_MIN Ta Dv LONG_MAX
.It Fn strtoll Ta Dv LLONG_MIN Ta Dv LLONG_MAX
.It Fn strtoimax Ta Dv INTMAX_MIN Ta Dv INTMAX_MAX
.It Fn strtoq Ta Dv LLONG_MIN Ta Dv LLONG_MAX
.El
.Pp
If there is no valid digit, 0 is returned.
If
.Ar base
is invalid, 0 is returned and the global variable
.Va errno
is set to
.Er EINVAL .
.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 strtol ,
and the return value of
.Fn strtol
cannot be used unambiguously to signal an error:
.Bd -literal -offset indent
char *ep;
long lval;

\&...

errno = 0;
lval = strtol(buf, &ep, 10);
if (buf[0] == '\e0' || *ep != '\e0')
	goto not_a_number;
if (errno == ERANGE && (lval == LONG_MAX || lval == LONG_MIN))
	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 .
.Pp
If
.Fn strtol
is being used instead of
.Xr atoi 3 ,
error checking is further complicated because the desired return value is an
.Vt int
rather than a
.Vt long ;
however, on some architectures integers and long integers are the same size.
Thus the following is necessary:
.Bd -literal -offset indent
char *ep;
int ival;
long lval;

\&...

errno = 0;
lval = strtol(buf, &ep, 10);
if (buf[0] == '\e0' || *ep != '\e0')
     goto not_a_number;
if ((errno == ERANGE && (lval == LONG_MAX || lval == LONG_MIN)) ||
    (lval > INT_MAX || lval < INT_MIN))
     goto out_of_range;
ival = lval;
.Ed
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EINVAL
The value of
.Ar base
was neither between 2 and 36 inclusive nor 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 sscanf 3 ,
.Xr strtod 3 ,
.Xr strtonum 3 ,
.Xr strtoul 3
.Sh STANDARDS
The
.Fn strtol ,
.Fn strtoll ,
and
.Fn strtoimax
functions conform to
.St -isoC-99 .
Setting
.Va errno
to
.Dv EINVAL
is an extension to that standard required by
.St -p1003.1-2008 .
.Pp
The
.Fn strtoq
function is a
.Bx
extension and is provided for backwards compatibility with legacy programs.
.Sh BUGS
Ignores the current locale.