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 must 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  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.   Pre-
       cisely  the same holds for strtoll() (with LLONG_MIN and LLONG_MAX
       instead of LONG_MIN and LONG_MAX).

ERRORS
       ERANGE The resulting value was out of range.

       EINVAL (not in C99) The given base contains an unsupported  value.

       The implementation may also set errno to EINVAL in case no conver-
       sion was performed (no digits seen, and 0 returned).

NOTES
       In locales other than the "C" locale, also other  strings  may  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 strtol().

CONFORMING TO
       strtol() conforms to SVID 3, BSD 4.3, ISO 9899  (C99)  and  POSIX,
       and strtoll() to ISO 9899 (C99) and POSIX 1003.1-2001.

SEE ALSO
       atof(3), atoi(3), atol(3), strtod(3), strtoul(3)



GNU                               2002-05-30                         STRTOL(3)

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

int my_atoi(char *str)
{
  char *p;
  int rv = 0, mult = 1, neg = 1;

  if(*str == '-')
  {
    p = ++str;
    neg = -1;
  }
  else
    p = str;

  while(isdigit(*p))
    p++;

  p--;

  while(p >= str)
  {
    rv += (*p - '0') * mult;
    mult *= 10;
    p--;
  }

  return rv * neg;
}

int main(int argc, char *argv[])
{
  if(argc != 2)
  {
    puts("Usage: myprog <number>");
    return 1;
  }

  printf("stdlib's atoi(): %d\n", atoi(argv[1]));
  printf("my my_atoi(): %d\n", my_atoi(argv[1]));

  return 0;
}