man-pages/man3/strtol.3

.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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.\" 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  2002-05-30 "GNU" "Linux Programmer's Manual"
.SH NAME
strtol, strtoll, strtoq \- convert a string to a long integer
.SH SYNOPSIS
.nf
.B #include <stdlib.h>
.sp
.BI "long int"
.BI "strtol(const char *" nptr ", char **" endptr ", int " base );
.sp
.BI "long long int"
.BI "strtoll(const char *" nptr ", char **" endptr ", int " base );
.fi
.SH DESCRIPTION
The
.BR strtol ()
function converts the initial part of the string
in \fInptr\fP to a long integer value according to the given \fIbase\fP,
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
.BR isspace (3))
followed by a single optional '+' or '\-' sign.
If \fIbase\fP is zero or 16, the string may then include a
"0x" prefix, and the number will be read in base 16; otherwise, a
zero \fIbase\fP is taken as 10 (decimal) unless the next character
is '0', in which case it is taken as 8 (octal).
.PP
The remainder of the string is converted to a
.I long int
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 'A' in
either upper or lower case represents 10, 'B' represents 11, and so
forth, with 'Z' representing 35.)
.PP
If \fIendptr\fP is not NULL,
.BR strtol ()
stores the address of the
first invalid character in \fI*endptr\fP.
If there were no digits at
all,
.BR strtol ()
stores the original value of \fInptr\fP in
\fI*endptr\fP (and returns 0).
In particular, if \fI*nptr\fP is not '\\0' but \fI**endptr\fP
is '\\0' on return, the entire string is valid.
.PP
The
.BR strtoll ()
function works just like the
.BR strtol ()
function but returns a 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, \fIerrno\fP 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
.TP
.B EINVAL
(not in C99)
The given
.I base
contains an unsupported value.
.TP
.B ERANGE
The resulting value was out of range.
.LP
The implementation may also set \fIerrno\fP to \fBEINVAL\fP in case
no conversion was performed (no digits seen, and 0 returned).
.SH "CONFORMING TO"
.BR strtol ()
conforms to SVr4, 4.3BSD, C89, C99 and POSIX.1-2001, and
.BR strtoll ()
to C99 and POSIX.1-2001.
.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
has a non-zero value after the call.

In locales other than the "C" locale, other strings may also be accepted.
(For example, the thousands separator of the current locale may be
supported.)
.LP
BSD also has
.sp
.in +4n
.nf
.BI "quad_t"
.BI "strtoq(const char *" nptr ", char **" endptr ", int " base );
.sp
.in -4n
.fi
with completely analogous definition.
Depending on the wordsize of the current architecture, this
may be equivalent to
.BR strtoll ()
or to
.BR strtol ().
.SH EXAMPLE
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:
.in +0.25i
.nf

$ ./a.out 123
strtol() returned 123
$ ./a.out '    123'
strtol() returned 123
$ ./a.out 123abc
strtol() returned 123
Further characters after number: abc
$ ./a.out 123abc 55
strtol: Invalid argument
$ ./a.out ''
No digits were found
$ ./a.out 4000000000
strtol: Numerical result out of range

.fi
.in -0.25i
The source code of the program is as follows:
.nf

#include <stdlib.h>
#include <limits.h>
#include <stdio.h>
#include <errno.h>

int
main(int argc, char *argv[])
{
    int base;
    char *endptr, *str;
    long val;

    if (argc < 2) {
        fprintf(stderr, "Usage: %s str [base]\\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    str = argv[1];
    base = (argc > 2) ? atoi(argv[2]) : 10;

    errno = 0;    /* To distinguish success/failure after call */
    val = strtol(str, &endptr, base);

    /* Check for various possible errors */

    if ((errno == ERANGE && (val == LONG_MAX || val == LONG_MIN))
            || (errno != 0 && val == 0)) {
        perror("strtol");
        exit(EXIT_FAILURE);
    }

    if (endptr == str) {
        fprintf(stderr, "No digits were found\\n");
        exit(EXIT_FAILURE);
    }

    /* If we got here, strtol() successfully parsed a number */

    printf("strtol() returned %ld\\n", val);

    if (*endptr != '\\0')        /* Not necessarily an error... */
        printf("Further characters after number: %s\\n", endptr);

    exit(EXIT_SUCCESS);
}
.fi
.SH "SEE ALSO"
.BR atof (3),
.BR atoi (3),
.BR atol (3),
.BR strtod (3),
.BR strtoul (3)