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

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.\"	$OpenBSD: strtol.3,v 1.6 1999/09/14 03:59:55 pjanzen Exp $
.\"
.Dd June 25, 1992
.Dt STRTOL 3
.Os
.Sh NAME
.Nm strtol, strtoq
.Nd convert string value to a long or quad_t integer
.Sh SYNOPSIS
.Fd #include <stdlib.h>
.Fd #include <limits.h>
.Ft long
.Fn strtol "const char *nptr" "char **endptr" "int base"

.Fd #include <sys/types.h>
.Fd #include <stdlib.h>
.Fd #include <limits.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
.Li long
value.
The
.Fn strtoq
function
converts the string in
.Fa nptr
to a
.Li 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 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 a
.Li long
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 nil,
.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
function
returns the result of the conversion,
unless the value would underflow or overflow.
If an underflow occurs,
.Fn strtol
returns
.Dv LONG_MIN .
If an overflow occurs,
.Fn strtol
returns
.Dv LONG_MAX .
In both cases,
.Va errno
is set to
.Er ERANGE .
.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
.Li int
rather than a
.Li 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 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 sscanf 3 ,
.Xr strtod 3 ,
.Xr strtoul 3
.Sh STANDARDS
The
.Fn strtol
function
conforms to
.St -ansiC .
.Sh BUGS
Ignores the current locale.