.\" Copyright (c) 1990, 1991 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" Chris Torek and the American National Standards Committee X3,
.\" on Information Processing Systems.
.\"
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.\" modification, are permitted provided that the following conditions
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.\" 3. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\"	$OpenBSD: strtol.3,v 1.15 2006/03/29 20:10:52 grunk Exp $
.\"
.Dd January 3, 2006
.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
.Fd #include <stdlib.h>
.Fd #include <limits.h>
.Ft long
.Fn strtol "const char *nptr" "char **endptr" "int base"
.Pp
.Ft long long
.Fn strtoll "const char *nptr" "char **endptr" "int base"
.Pp
.Fd #include <inttypes.h>
.Ft intmax_t
.Fn strtoimax "const char *nptr" "char **endptr" "int base"
.Pp
.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 strtoll
function converts the string in
.Fa nptr
to a
.Li long long
value.
The
.Fn strtoimax
function converts the string in
.Fa nptr
to an
.Li 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
.Li long ,
.Li long long ,
or
.Li 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 returns the result of the conversion,
unless the value would underflow or overflow.
If overflow or underflow occurs,
.Va errno
is set to
.Er ERANGE
and the function return value is as follows:
.Bl -column -offset indent "strtoimax" "overflow" "underflow"
.It Sy Function Ta Sy overflow Ta Sy underflow
.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
.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 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 -ansiC-99 .
The
.Fn strtoq
function is a
.Bx
extension and is provided for backwards compatibility with legacy programs.
.Sh BUGS
Ignores the current locale.