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
   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"
   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
   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().

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 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), strtoul(3)

COLOPHON

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   description of the project, information about reporting bugs,  and  the
   latest     version     of     this    page,    can    be    found    at
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