Re: Processing command line arguments

On Apr 21, 10:52 am, "Malcolm McLean" <regniz...@xxxxxxxxxxxxxx>
wrote:
"Gregor H." <nomail@invalid> wrote in message

(Why did you start a new thread to reply to this question?)

news:maij2396rr5qli9a1lndf3cv5g4g5mgjpr@xxxxxxxxxx

In K&R (2nd edition) the authors published the following code for
dealing with command line arguments (p. 117):

while (--argc > 0 && (*++argv)[0] == '-')
while (c = *++argv[0])
switch (c) {
case 'x':
except = 1;
break;
case 'n':
number = 1;
break;
default:
printf("find: illegal option %c\n", c);
argc = 0;
found = -1;
break;
}

But this solution raised some criticism:

"The sample program incrementsargv[0]. Althoughargvis
modifiable, andargv[0][0] is modifiable (ifargv[0] is
not a null pointer),argv[0] is not modifiable. (At least,
not always.)"

(Peter Seebacher,http://www.plethora.net/~seebs/c/knr.html)

"p.117 (§5.10): In the find example, the program increments
argv[0]. This is not specifically forbidden, but not
specifically allowed either."

(Source:
Errata for The C Programming Language, Second Edition
http://cm.bell-labs.com/cm/cs/cbook/2ediffs.html)

Now my question is: would the following (slight modification of the
original code) be a reasonable (or at least correct) solution?:

while (--argc > 0 && (*++argv)[0] == '-') {

This line is virtually unreadable. I know K and R used the same construct.
Things have moved on.

Say what? It's terse, clear, and correct - what more can you ask for
in a line of code?

char *arg = *argv;
while (c = *++arg)

However this is the way round.argvcontains a list of strings. Nothing
conceptually difficult about that, but you can make it look difficult
because strigns are not atomic objects in C. It is a bad idea to modify the
strings in place, though I think they are writeable for historical reasons,
and it is a bad idea and may even be illegal to modify the pointers in theargvarray.
However if you take copies then you can do what you want with the copy,
naturally.
--
Free games and programming goodies.http://www.personal.leeds.ac.uk/~bgy1mm


.

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