Chapter Contents

Previous

Next

strtol

Portability:

ISO/ANSI C conforming, UNIX compatible

SYNOPSIS

#include <stdlib.h>

long int strtol(const char *str, char **end, int radix);

DESCRIPTION

strtol converts a character string to a long integer. The string is expected to contain the representation of an integer in base radix . Base radix can 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 initial characters 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 NULL , *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

strtol returns the 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, 0L is returned.

DIAGNOSTICS

If the correct value is too large to be stored in a 370 long , errno is set to ERANGE and either LONG_MAX (2³¹-1) or LONG_MIN (-2³¹) is returned, depending on the sign of the value.

EXAMPLE

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

long int hextol(char *);
static int failed;

main()
{
   char *string;
   char input[20];
   long output;
   puts("Enter a hex string to convert to long int:");
   string = gets(input);
   output = hextol(string);
   if (!failed)
      printf("The value of the string, printed in decimal, is: %ld\n",
              output);
}

long int hextol(char *hexstr)
{
   long value;
   char *stopchar;    /* where strtol conversion stops */

      /* 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 -1L;
   }

      /* Convert hex to long.                          */
   value = strtol(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

strtod , strtoul

SEE ALSO

• String Utility Functions

Chapter Contents

Previous

Next

Top of Page

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