Re^2: XS malloc and free (whose)

Not easy indeed. None of the following work:

#define d a

#include <stdio.h>

void a() { printf("a\n"); }
void b() { printf("b\n"); }

int main() {
   a();
#define a b
   a();

   (*&a)();

   /* \a(); */

#define c a
   c();

   d();

   return 0;
}
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Comment on Re^2: XS malloc and free (whose) Download Code

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Re^3: XS malloc and free (whose) by tye (Sage) on Feb 07, 2006 at 20:17 UTC
Of course not. (: The C preprocessor is mostly just text substitution and is defined to not care about the order in which things are defined. A more interesting case that also doesn't work is: `#include <stdio.h> void flee(int i) { printf("flee(%d)\n",i); } void perlFlee(int i) { printf("perlFlee(%d)\n",i); } int main() { flee(1); #define flee perlFlee flee(2); #define _stitch(a,b) a ## b #define Free(x) _stitch(fl,ee)( x ) Free(3); return 0; }` [download] Which produces "`perlFlee(3)`" as its last line of output. And this tenancity of the C preprocessor is why (at least when the idea of XS came about), there should have been (similar to several other changes that were made for similar reasons) a global `s/\bfree\b/Perl_free/`, and `s/\bmalloc\b/Perl_malloc/g` done to the Perl source code so "`#define free`..." could be eliminated (replaced with "`#define Perl_free free`" for some systems, of course). - tye	[reply] [d/l] [select]

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Re^3: XS malloc and free (whose)
by tye (Sage) on Feb 07, 2006 at 20:17 UTC

Of course not. (: The C preprocessor is mostly just text substitution and is defined to not care about the order in which things are defined.

A more interesting case that also doesn't work is:

#include <stdio.h>

void flee(int i)     { printf("flee(%d)\n",i); }
void perlFlee(int i) { printf("perlFlee(%d)\n",i); }

int main()
{
   flee(1);
#define flee perlFlee
   flee(2);

#define _stitch(a,b) a ## b
#define Free(x) _stitch(fl,ee)( x )
   Free(3);

   return 0;
}
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Which produces "perlFlee(3)" as its last line of output.

And this tenancity of the C preprocessor is why (at least when the idea of XS came about), there should have been (similar to several other changes that were made for similar reasons) a global s/\bfree\b/Perl_free/, and s/\bmalloc\b/Perl_malloc/g done to the Perl source code so "#define free..." could be eliminated (replaced with "#define Perl_free free" for some systems, of course).

- tye

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