Manpage of STRTOL

STRTOL

Section: Linux Programmer's Manual (3)
Updated: 2016-03-15
Index
 

NAME

strtol, strtoll, strtoq - convert a string to a long integer  

SYNOPSIS

#include <stdlib.h>long int strtol(const char *nptr, char **endptr, int base);long long int strtoll(const char *nptr, char **endptr, int base);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

strtoll():

_ISOC99_SOURCE
    || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
 

DESCRIPTION

The strtol() function converts the initial part of the string in nptrto a long integer value according to the given base, which must be between 2 and 36 inclusive, or be the special value 0.

The string may begin with an arbitrary amount of white space (as determined by isspace(3)) followed by a single optional aq+aq or aq-aq sign. If baseis zero or 16, the string may then include a "0x" prefix, and the number will be read in base 16; otherwise, a zero baseis taken as 10 (decimal) unless the next character is aq0aq, in which case it is taken as 8 (octal).

The remainder of the string is converted to a long intvalue 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 aqAaq in either uppercase or lowercase represents 10, aqBaq represents 11, and so forth, with aqZaq representing 35.)

If endptris not NULL, strtol() stores the address of the first invalid character in *endptr. If there were no digits at all, strtol() stores the original value of nptrin *endptr(and returns 0). In particular, if *nptris not aq\0aq but **endptris aq\0aq on return, the entire string is valid.

The strtoll() function works just like the strtol() function but returns a long long integer value.  

RETURN VALUE

The strtol() function returns the result of the conversion, unless the value would underflow or overflow. If an underflow occurs, strtol() returns LONG_MIN. If an overflow occurs, strtol() returns LONG_MAX. In both cases, errnois set to ERANGE. Precisely the same holds for strtoll() (with LLONG_MINand LLONG_MAXinstead of LONG_MINand LONG_MAX).  

ERRORS

EINVAL
(not in C99) The given basecontains an unsupported value.
ERANGE
The resulting value was out of range.

The implementation may also set errnoto EINVALin case no conversion was performed (no digits seen, and 0 returned).  

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).
InterfaceAttributeValue
strtol(), strtoll(), strtoq() Thread safetyMT-Safe locale
 

CONFORMING TO

strtol(): POSIX.1-2001, POSIX.1-2008, C89, C99 SVr4, 4.3BSD.

strtoll(): POSIX.1-2001, POSIX.1-2008, C99.  

NOTES

Since strtol() can legitimately return 0, LONG_MAX, or LONG_MIN(LLONG_MAXor LLONG_MINfor strtoll()) on both success and failure, the calling program should set errnoto 0 before the call, and then determine if an error occurred by checking whether errnohas a nonzero value after the call.

According to POSIX.1, in locales other than the "C" and "POSIX", these functions may accept other, implementation-defined numeric strings.

BSD also has

quad_t strtoq(const char *nptr, char **endptr, int base);
with completely analogous definition. Depending on the wordsize of the current architecture, this may be equivalent to strtoll() or to strtol().  

EXAMPLE

The program shown below demonstrates the use of strtol(). The first command-line argument specifies a string from which 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 atoi(3), a function that performs no error checking and has a simpler interface than strtol().) Some examples of the results produced by this program are the following:
$ ./a.out 123strtol() returned 123
$ ./a.out aq    123aqstrtol() returned 123
$ ./a.out 123abcstrtol() returned 123
Further characters after number: abc
$ ./a.out 123abc 55strtol: Invalid argument
$ ./a.out aqaqNo digits were found
$ ./a.out 4000000000strtol: Numerical result out of range
 

Program source

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

    exit(EXIT_SUCCESS);
}
 

SEE ALSO

atof(3), atoi(3), atol(3), strtod(3), strtoul(3)


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
ATTRIBUTES
CONFORMING TO
NOTES
EXAMPLE
Program source
SEE ALSO

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Time: 22:27:59 GMT, June 20, 2016