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Internet Message Format | 1996-08-05 | 2.8 KB

Path: ix.netcom.com!netnews
From: [e-mail] (Mike Rubenstein)
Newsgroups: comp.lang.c
Subject: Re: simple code, argc, argv, strcmp()
Date: Thu, 01 Feb 1996 12:50:27 GMT
Organization: Netcom
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[e-mail] (Otis Gospodnetic) wrote:

> Hi, a C question...
> this one has been bothering ALL afternoon !
>
> This snippet of code is supposed to call appropriate function based on what
> command line arguments are supplied.
>
> usage: <program> -e [SourceFile] RemoteFile
>         or
>        <program> -d [InFile]
>
> if the person doesn't use this right the program is supposed to call Usage()
> which is not here, but it's in my code, and if the person calls the program
> the correct way one of the two actions should be taken (encode or decode).
>
> Problem - I am doing something wrong and I almost always end up calling
> Usage() even if I use the program correctly.
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
>
> int main (int argc, char **argv) {
>
>   void Usage   (void);
>   void Encode (int, char **);
>   void Decode (int, char **);
>
>   if (!strcmp(argv[1],"-d") || !strcmp(argv[1],"-e")) {
>     Usage();
>   }
>   if (strcmp(argv[1],"-d") && argc < 3) {
>     printf ("D %i\n", argc);
>     Usage();
>   }
>   if (strcmp(argv[1],"-e") && argc < 4) {
>     printf ("E %i\n", argc);
>     Usage();
>   }
>   if (strcmp(argv[1],"-d") && argc == 3) {
>     Decode(argc, argv);
>   }
>   if (strcmp(argv[1],"-e") && argc == 4) {
>     Encode(argc, argv);
>   }
>   return 0;
> }
>
> Can someone see what's wrong with this ?
> am I not using strcmp() right ?
>
> Thanks a bunch (I don't have any more hair to pull from my head !)

You've got a few problems.

When you think there's a problem with your use of a function, the
first step should be to read the manual and find out what it really
does.  strcmp() returns 0 if the strings are equal, negative if the
first compares less than the second, positive if the first compares
greater.  You seem to be assuming it will return nonzero if they are
equal.

Even when you correct that, your first test will be incorrect.  Think
about what it is doing -- you seem to be trying to test whether the
first command line argument is either not equal to -d or not equal to
-e.  This will be true for all possible command line arguments.

Finally, think about what happens if there are too many command line
arguments.  You try to call Usage() if there are too few and call the
appropriate function if there are the right number, but simply return
if there are too many.


Michael M Rubenstein