Chapter Contents

Previous

Next

strtoul

Portability:

ISO/ANSI C conforming

SYNOPSIS

#include <stdlib.h>

unsigned long int strtoul(const char *str, char **end, int base);

DESCRIPTION

strtoul converts a character string to an unsigned long integer. The string is expected to contain the representation of an unsigned integer in base radix . Base radix may contain an integer between 2 and 36; if it is larger than 10, letters 'a' through 'z' (either case) are interpreted as digits greater than 10. If radix is 16, a leading 0x may be present in the string, but it is ignored. Initial white space characters are always ignored.

If radix is 0, the base is determined by the first character of the string (after leading white space and an optional sign). That is, if the string begins with 0x or 0X, the base is assumed to be 16; if it begins with 0, it is assumed to be 8; otherwise, it is assumed to be 10.

If the end value is not 0, *end is modified to address the first character of the string that is not a valid base radix digit. However, if no initial segment of the string can be interpreted as an integer of appropriate base, str is assigned to *end .

RETURN VALUE

strtoul returns the unsigned integer value represented by the character string up to the first unrecognized character. If no initial segment of the string can be interpreted as an integer of appropriate base, 0UL is returned.

DIAGNOSTICS

If the correct value is too large to be stored in a 370 unsigned long , errno is set to ERANGE, and 2³²-1 is returned. (This is the value of ULONG_MAX , defined in <limits.h> .)

EXAMPLE

#include <stdlib.h>
#include <ctype.h>
#include <stdio.h>

unsigned long hextoul(char *);
static int failed;

main()
{
   char *string;
   char input[20];
   unsigned long output;
   puts("Enter a hex string to convert to unsigned long int:");
   string = gets(input);
   output = hextoul(string);
   if (!failed)
      printf("The string is converted to: %ld\n", output);
}

unsigned long hextoul(char * a)
{
   unsigned long value;
   char *hexstr;     /* hexadecimal input string       */
   char *stopchar;   /* where strtoul conversion stops */
   hexstr = a;

      /* Skip space characters.                        */
   while(isspace(*hexstr)) ++hexstr;

      /* Skip leading 0x.                              */
   if (*hexstr == '0' && tolower(*(hexstr+1)) == 'x')
      hexstr += 2;

      /* refused signed hex value                      */
   if (*hexstr == '+' || *hexstr == '-') {
      puts("Unsigned hex only please");
      failed = 1;
      return -1UL;
   }
      /* Convert hex to long.                          */
   value = strtoul(hexstr, &stopchar, 16);

      /* Determine whether string is valid.            */
   if (stopchar == hexstr) {
      printf("Invalid hex string: %s\n", hexstr);
      failed = 1;
   }
      /* Check for characters after digits.            */
   else if (*stopchar && !isspace(*stopchar))
      printf("Extra characters after hex value ignored: %s\n",
              stopchar);

   return value;
}

RELATED FUNCTIONS

strtol

SEE ALSO

• String Utility Functions

Chapter Contents

Previous

Next

Top of Page

Copyright © 2001 by SAS Institute Inc., Cary, NC, USA. All rights reserved.