path: root/man/man3/strtol.3

'\" t
.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\" and Copyright 2006 Michael Kerrisk <mtk.manpages@ganil.com>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified Sun Jul 25 10:53:39 1993 by Rik Faith (faith@cs.unc.edu)
.\" Added correction due to nsd@bbc.com (Nick Duffek) - aeb, 950610
.TH strtol 3 2024-05-02 "Linux man-pages (unreleased)"
.SH NAME
strtol, strtoll, strtoq \- convert a string to a long integer
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <stdlib.h>
.P
.BI "long strtol(const char *restrict " nptr ,
.BI "            char **restrict " endptr ", int " base );
.BI "long long strtoll(const char *restrict " nptr ,
.BI "            char **restrict " endptr ", int " base );
.fi
.P
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.P
.BR strtoll ():
.nf
    _ISOC99_SOURCE
        || /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
.fi
.SH DESCRIPTION
The
.BR strtol ()
function converts the initial part of the string
in
.I nptr
to a long integer value according to the given
.IR base ,
which must be between 2 and 36 inclusive, or be the special value 0.
.P
The string may begin with an arbitrary amount of white space (as
determined by
.BR isspace (3))
followed by a single optional \[aq]+\[aq] or \[aq]\-\[aq] sign.
If
.I base
is zero or 16, the string may then include a
"0x" or "0X" prefix, and the number will be read in base 16; otherwise, a
zero
.I base
is taken as 10 (decimal) unless the next character
is \[aq]0\[aq], in which case it is taken as 8 (octal).
.P
The remainder of the string is converted to a
.I 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 \[aq]A\[aq] in
either uppercase or lowercase represents 10, \[aq]B\[aq] represents 11, and so
forth, with \[aq]Z\[aq] representing 35.)
.P
If
.I endptr
is not NULL,
and the
.I base
is supported,
.BR strtol ()
stores the address of the
first invalid character in
.IR *endptr .
If there were no digits at
all,
.BR strtol ()
stores the original value of
.I nptr
in
.I *endptr
(and returns 0).
In particular, if
.I *nptr
is not \[aq]\e0\[aq] but
.I **endptr
is \[aq]\e0\[aq] on return, the entire string is valid.
.P
The
.BR strtoll ()
function works just like the
.BR strtol ()
function but returns a
.I long long
integer value.
.SH RETURN VALUE
The
.BR strtol ()
function returns the result of the conversion,
unless the value would underflow or overflow.
If an underflow occurs,
.BR strtol ()
returns
.BR LONG_MIN .
If an overflow occurs,
.BR strtol ()
returns
.BR LONG_MAX .
In both cases,
.I errno
is set to
.BR ERANGE .
Precisely the same holds for
.BR strtoll ()
(with
.B LLONG_MIN
and
.B LLONG_MAX
instead of
.B LONG_MIN
and
.BR LONG_MAX ).
.SH ERRORS
This function does not modify
.I errno
on success.
.TP
.B EINVAL
(not in C99)
The given
.I base
contains an unsupported value.
.TP
.B ERANGE
The resulting value was out of range.
.P
The implementation may also set
.I errno
to
.B EINVAL
in case
no conversion was performed (no digits seen, and 0 returned).
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.na
.nh
.BR strtol (),
.BR strtoll (),
.BR strtoq ()
T}	Thread safety	MT-Safe locale
.TE
.SH STANDARDS
C11, POSIX.1-2008.
.SH HISTORY
.TP
.BR strtol ()
POSIX.1-2001, C89, SVr4, 4.3BSD.
.TP
.BR strtoll ()
POSIX.1-2001, C99.
.SH NOTES
Since
.BR strtol ()
can legitimately return 0,
.BR LONG_MAX ,
or
.B LONG_MIN
.RB ( LLONG_MAX
or
.B LLONG_MIN
for
.BR strtoll ())
on both success and failure, the calling program should set
.I errno
to 0 before the call,
and then determine if an error occurred by checking whether
.I errno == ERANGE
after the call.
.P
According to POSIX.1,
in locales other than "C" and "POSIX",
these functions may accept other,
implementation-defined numeric strings.
.P
BSD also has
.P
.in +4n
.EX
.BI "quad_t strtoq(const char *" nptr ", char **" endptr ", int " base );
.EE
.in
.P
with completely analogous definition.
Depending on the wordsize of the current architecture, this
may be equivalent to
.BR strtoll ()
or to
.BR strtol ().
.SH CAVEATS
If the
.I base
needs to be tested,
it should be tested in a call where the string is known to succeed.
Otherwise, it's impossible to portably differentiate the errors.
.P
.in +4n
.EX
errno = 0;
strtol("0", NULL, base);
if (errno == EINVAL)
    goto unsupported_base;
.EE
.in
.SH EXAMPLES
The program shown below demonstrates the use of
.BR strtol ().
The first command-line argument specifies a string from which
.BR strtol ()
should parse a number.
The second (optional) argument specifies the base to be used for
the conversion.
(This argument is converted to numeric form using
.BR atoi (3),
a function that performs no error checking and
has a simpler interface than
.BR strtol ().)
Some examples of the results produced by this program are the following:
.P
.in +4n
.EX
.RB "$" " ./a.out 123"
strtol() returned 123
.RB "$" " ./a.out \[aq]    123\[aq]"
strtol() returned 123
.RB "$" " ./a.out 123abc"
strtol() returned 123
Further characters after number: "abc"
.RB "$" " ./a.out 123abc 55"
strtol: Invalid argument
.RB "$" " ./a.out \[aq]\[aq]"
No digits were found
.RB "$" " ./a.out 4000000000"
strtol: Numerical result out of range
.EE
.in
.SS Program source
\&
.\" SRC BEGIN (strtol.c)
.EX
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
\&
int
main(int argc, char *argv[])
{
    int base;
    char *endptr, *str;
    long val;
\&
    if (argc < 2) {
        fprintf(stderr, "Usage: %s str [base]\en", argv[0]);
        exit(EXIT_FAILURE);
    }
\&
    str = argv[1];
    base = (argc > 2) ? atoi(argv[2]) : 0;
\&
    errno = 0;    /* To distinguish success/failure after call */
    strtol("0", NULL, base);
    if (errno == EINVAL) {
        perror("strtol");
        exit(EXIT_FAILURE);
    }
\&
    errno = 0;    /* To distinguish success/failure after call */
    val = strtol(str, &endptr, base);
\&
    /* Check for various possible errors. */
\&
    if (errno == ERANGE) {
        perror("strtol");
        exit(EXIT_FAILURE);
    }
\&
    if (endptr == str) {
        fprintf(stderr, "No digits were found\en");
        exit(EXIT_FAILURE);
    }
\&
    /* If we got here, strtol() successfully parsed a number. */
\&
    printf("strtol() returned %ld\en", val);
\&
    if (*endptr != \[aq]\e0\[aq])        /* Not necessarily an error... */
        printf("Further characters after number: \e"%s\e"\en", endptr);
\&
    exit(EXIT_SUCCESS);
}
.EE
.\" SRC END
.SH SEE ALSO
.BR atof (3),
.BR atoi (3),
.BR atol (3),
.BR strtod (3),
.BR strtoimax (3),
.BR strtoul (3)