Date: Mon, 21 May 2001 17:04:35 -0500 From: John Joseph Trammell <trammell@trammell.dyndns.org> To: freebsd-questions@freebsd.org Subject: Re: Question for C preprocessor gurus Message-ID: <20010521170435.A1610@mn.rr.com> In-Reply-To: <11895256.990483991242.JavaMail.imail@zero.excite.com>; from john_wilson100@excite.com on Mon, May 21, 2001 at 03:26:30PM -0700 References: <11895256.990483991242.JavaMail.imail@zero.excite.com>
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On Mon, May 21, 2001 at 03:26:30PM -0700, John Wilson wrote:
> In this program I'm writing, I need to define a simple list of errors, e.g.
>
> #define ERR_OK 0
> #define ERR_BAD 1
> #define ERR_AWFUL 2
>
> and a function to return error descriptions:
>
> char *f(int error_no)
> {
> switch (error_no)
> {
> case ERR_OK:
> return "OK";
>
> case ERR_BAD:
> return "Bad";
>
> /* .... */
> }
> }
>
>
> There is nothing wrong with this code, except one thing - to add a new
> error, I need to do it in two different places. I was therefore wondering
> if it was possible to avoid adding the same strings twice through (ab)use of
> the preprocessor.
How about defining the error values/symbols/messages in a text file,
then generating the .c and .h files dynamically?
[ ~/test/errno-001 ] cat errors.txt
0 ERR_OK okily-dokily!
1 ERR_BAD abandon ship!
2 ERR_AWFUL my hovercraft is full of eels!
[ ~/test/errno-001 ] cat gencode.pl
use strict;
my @lines;
while (<>) { chomp; push @lines, $_ }
# make .h file
open(FOO,">foo.h") or die "Can't open foo.h for writing: $!";
for (@lines)
{
my ($num,$sym) = (split(' ',$_,3))[0,1];
print FOO "#define $sym $num\n";
}
close FOO;
# make .c file
open(FOO,">foo.c") or die "Can't open foo.c for writing: $!";
print FOO "char *f(int e) { switch (e) {\n";
for (@lines)
{
my ($sym,$text) = (split(' ',$_,3))[1,2];
print FOO "\tcase $sym: return \"$text\";\n";
}
print FOO "}}\n";
close FOO;
[ ~/test/errno-001 ] perl -w gencode.pl errors.txt
[ ~/test/errno-001 ] cat foo.h foo.c
#define ERR_OK 0
#define ERR_BAD 1
#define ERR_AWFUL 2
char *f(int e) { switch (e) {
case ERR_OK: return "okily-dokily!";
case ERR_BAD: return "abandon ship!";
case ERR_AWFUL: return "my hovercraft is full of eels! ";
}}
[ ~/test/errno-001 ]
--
If you don't look at the fnord, it can't get you.
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