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 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 nptr
       to a long integer value according to the given base, which must be  be-
       tween 2 and 36 inclusive, or be the special value 0.

       The string may begin with an arbitrary amount of white space (as deter-
       mined 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 int value in the ob-
       vious  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  re-
       turns 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 at-
       tributes(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  deter-
       mine 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  str-
       tol().

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  pro-
       duced 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]) : 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);
       }

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

COLOPHON
       This  page  is  part of release 5.05 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                               2019-10-10                         STRTOL(3)