strtol

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 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 charac-        ter 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). 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 check-        ing 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

#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);
}

atoi 보다 막강한 함수라고 한다.

[링크 : http://en.wikipedia.org/wiki/Strtol]
[링크 : http://linux.die.net/man/3/strtol]