Re: getopt() library function options

["J." <mailing-lists@xs4all.nl>]

On Sat, 5 Mar 2005, Rechberger Markus wrote:

> Hey,

Hey.. ;-)
 
> regarding atoi:
> 
> #include <stdio.h>

#include <stdlib.h>

> int main(){
>         printf("value: %d\n",atoi("nosegv123"));
>         return(0);
> }
> output:
> value: 0
> 
> this doesn't segfault

Yes, - atoi in stdlib.h is actually strtol...

But, the answer was about using atoi in combination with 
getopt(), maybe it was my lack of explanation sorry...
Anyway, atoi(optarg) while there is no optarg will segfault...
Then, you will always want to check for digits, since atoi 
can't determine the difference inbetween the argument `0' 
or "nosegv123" . atoi returns the same value for both, thus `0' .

If your program checks something INT times and atoi returns `0'
even on errorlike user input, the program will check `0' times..

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

int main(int argc, char *argv[]){
 char *str1 = "nosegv123";
 char *str2 = "0.012";
 char *str3 = "0";
 char *str4 = "-1";

 printf("str: %s - value: %d\n",str1, atoi(str1));
 printf("str: %s - value: %d\n",str2, atoi(str2));
 printf("str: %s - value: %d\n",str3, atoi(str3));
 printf("str: %s - value: %d\n",argv[1], atoi(argv[1]));
 printf("str: %s - value: %d\n",str4, atoi(str4));
 return(0);
}

> ctype only takes one variable as argument _not_ a string, he would
> have to check every element of the array with isdigit.

Yep.. But *pointers are quite cheap these days I hear.. ;-)

Thnkx..  J.

> > int isthisanint(char *str) {
> >  regex_t re;
> >  int retval = -1;
> > 
> >  setlocale(LC_ALL, "");
> >  if(regcomp(&re, "^([0-9]*)$", REG_EXTENDED) != 0) {
> >   fprintf(stderr, "%s: Error - Unable to compile regex", PACKAGE);
> >   return -1;
> >  }
> > 
> >  if(regexec(&re, str, 0, NULL, 0) != 0)
> >   retval = -1;
> >  else
> >   retval = atoi(str);
> > 
> >  /* or.. Like listed in the manual page */
> >  /*  strtol(nptr, (char **)NULL, 10); */
> > 
> >  regfree(&re);
> >  return retval;
> > }