strtol(3)



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);

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 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' 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
       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.)

       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).

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  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.)

       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().

CONFORMING TO
       strtol()  conforms to SVr4, 4.3BSD, C99 and POSIX.1-2001, and strtoll()
       to C99 and POSIX.1-2001.

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

       The source code of the program is as follows:

       #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), strtoul(3)

GNU                               2002-05-30                         STRTOL(3)

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