strtol

STRTOL(3)                   Linux Programmer's Manual                  STRTOL(3)



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

SYNOPSIS
       #include <stdlib.h>

       long strtol(const char *nptr, char **endptr, int base);

       long long 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 nptr to
       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 '+' or '-' sign.
       If 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 base is taken
       as 10 (decimal) unless the next character is '0', in which case it is
       taken as 8 (octal).

       The remainder of the string is converted to a 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 'A' in either uppercase or
       lowercase represents 10, 'B' represents 11, and so forth, with 'Z'
       representing 35.)

       If endptr is 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 nptr in *endptr (and returns 0).  In particular, if
       *nptr is not '\0' but **endptr is '\0' 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, errno is set to ERANGE.  Precisely the same holds for
       strtoll() (with LLONG_MIN and LLONG_MAX instead of LONG_MIN and
       LONG_MAX).

ERRORS
       EINVAL (not in C99) The given base contains an unsupported value.

       ERANGE The resulting value was out of range.

       The implementation may also set errno to EINVAL in 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).

       ┌──────────────────────────────┬───────────────┬────────────────┐
       │Interface                     Attribute     Value          │
       ├──────────────────────────────┼───────────────┼────────────────┤
       │strtol(), strtoll(), strtoq() │ Thread safety │ MT-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_MAX or LLONG_MIN for strtoll()) on both success and failure, the
       calling program should set errno to 0 before the call, and then determine
       if an error occurred by checking whether errno has 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().

EXAMPLES
       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 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

   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]) : 0;

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

           /* Check for various possible errors */

           if (errno != 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);
       }

SEE ALSO
       atof(3), atoi(3), atol(3), strtod(3), strtoimax(3), strtoul(3),

COLOPHON
       This page is part of release 5.09 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.



GNU                                2020-11-01                          STRTOL(3)