Date: Mon, 3 Apr 2000 18:34:18 +0200 From: Samuel Tardieu <sam@inf.enst.fr> To: John Polstra <jdp@polstra.com> Cc: bright@wintelcom.net, current@freebsd.org Subject: Re: MLEN and crashes Message-ID: <2000-04-03-18-34-19%2Btrackit%2Bsam@inf.enst.fr> In-Reply-To: <200004031622.JAA19715@vashon.polstra.com>; from jdp@polstra.com on Mon, Apr 03, 2000 at 09:22:09AM -0700 References: <Pine.BSF.4.21.0004022118510.1442-100000@alphplex.bde.org> <20000403084330.6A6DC483D@hcswork.hcs.de> <20000403023858.F21029@fw.wintelcom.net> <200004031622.JAA19715@vashon.polstra.com>
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On 3/04, John Polstra wrote:
| I doubt if it's possible to implement that at compile time. Remember,
| the preprocessor doesn't understand "sizeof". It doesn't recognize
| keywords in expressions at all.
Then don't use the preprocessor alone and use both the preprocessor and
the compiler. I suppose something like this will work:
struct foobar {
...;
}
#ifdef CHECK_STRUCT_SIZE
#define MAX_FOOBAR_SIZE 8
static char dummy_foobar [MAX_FOOBAR_SIZE-sizeof(struct foobar)];
#undef MAX_FOOBAR_SIZE
#endif
If sizeof(struct foobar) is more than MAX_FOOBAR_SIZE, then the compiler
will try to create an array with a negative size, which will not compile.
Embed this in a macro and you're done:
#ifdef CHECK_STRUCT_SIZE
#define CSS(S,T,U) static char dummy_##T [U-sizeof(S)];
#else
#define CSS(S,T,U)
#endif
Then use:
CSS(struct foobar,foobar,8)
Sam
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