Thread: I don't see the use of ifdef/endif in the following code

Given the following stripped down version of some production code..

Code:

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

#define MIN_LOGIN_LEN 2
#define MAX_LOGIN_LEN 32
int main(void)
{
  char lid[] = "c";

  #ifdef MIN_LOGIN_LEN
  if (strlen(lid) < MIN_LOGIN_LEN)
    {
      fprintf(stderr,"Login name must be at least %d characters long.\n",
              MIN_LOGIN_LEN);
      return 1;
    }
  #endif
    
  if (strlen(lid) > MAX_LOGIN_LEN)
    {
      fprintf(stderr,"Login name exceeds %d characters.\n",MAX_LOGIN_LEN);
      return 1;
    }

 return 0;
}

I get

[cdalten@localhost oakland]$ gcc -g cap3.c -o cap3
[cdalten@localhost oakland]$ ./cap3
Login name must be at least 2 characters long.
[cdalten@localhost oakland]$


Now, when I remove both MIN_LOGIN_LEN and define MAX_LOGIN_LEN in the following..

Code:

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

#define MIN_LOGIN_LEN 2
#define MAX_LOGIN_LEN 32
int main(void)
{
  char lid[] = "c";

  if (strlen(lid) < MIN_LOGIN_LEN)
    {
      fprintf(stderr,"Login name must be at least %d characters long.\n",
              MIN_LOGIN_LEN);
      return 1;
    }
    
  if (strlen(lid) > MAX_LOGIN_LEN)
    {
      fprintf(stderr,"Login name exceeds %d characters.\n",MAX_LOGIN_LEN);
      return 1;
    }

 return 0;
}

[cdalten@localhost oakland]$ gcc -g cap3.c -o cap3
[cdalten@localhost oakland]$ ./cap3
Login name must be at least 2 characters long.

I still get the same results. What is the point of the ifdef/endif in this case.

Okay, here is the snipped of code in question

Code:

#ifdef MIN_LOGIN_LEN
    if (strlen(lid) < MIN_LOGIN_LEN)
    {
        sprintf(msg,"Login name must be at least %d characters long.\n",
            MIN_LOGIN_LEN);
        return 1;
    }
#endif
    
    if (strlen(lid) > MAX_LOGIN_LEN)
    {
        sprintf(msg,"Login name exceeds %d characters.\n",MAX_LOGIN_LEN);
        return 1;
    }

    for (c= lid; *c != '\0'; c++)
#ifdef MIXED_CASE_LOGINS
        if (!isascii(*c) || !(isalpha(*c) || (c != lid && isdigit(*c))))
        {
            strcpy(msg,"Logins may contain only letters and digits, "
                "and begin with a letter.\n");
            return 1;
        }
#else
        if (!isascii(*c) || !(islower(*c) || (c != lid && isdigit(*c))))
        {
            strcpy(msg,"Logins may contain only lower-case letters and digits, "
                "and begin with a letter.\n");
            return 1;
        }
#endif /* !MIXED_CASE_LOGINS */

If the ifdef/endif don't matter, then why would have Dr. Weiss, the author of the program in question, go through the hassle of having them in the first place.

I think the point is that the #ifdef is a conditional inclusion. It seems odd that the MIN_LOGIN_LEN 2 would be #defined in the code itself. It would seem to be more reasonable that the #define would be done on the command line or in the makefile or whatever - that way you could either build the software with the min login length, or not, depending on what you wanted. By taking the #ifdef out in your second example, you are taking away the 'option' - the code is built with a minimum login length functionality. By including the #define in the first example, you are also negating the 'option,' because then the #ifdef is always true.