[Ccing bug-gnulib]
Sam Steingold asked:
> if I use alloca-opt from gnulib, can I replace
>
> #ifdef HAVE_ALLOCA
> #define alloca __builtin_alloca
> #elif defined(MICROSOFT)
> #include <malloc.h>
> #define alloca _alloca
> #elif defined(HAVE_ALLOCA_H)
> #include <alloca.h>
> #ifndef alloca /* some define 'alloca' as macro... */
> #if !(defined(UNIX_OSF) || defined(UNIX_DEC_ULTRIX))
> /* OSF/1 V3 declares `alloca' as returning char*, but in OSF/1 V4
> it returns void*. I don't know how to distinguish the two. */
> extern_C void* alloca (int size); /* see MALLOC(3V) */
> #endif
> #endif
> #elif defined(_AIX)
> #pragma alloca /* AIX requires this to be the first thing in the file. */
> #elif !defined(NO_ALLOCA)
> extern_C void* alloca (int size); /* see MALLOC(3V) */
> #endif
>
> with something like
>
> #include <alloca.h>
> #ifndef HAVE_ALLOCA
> #if defined(MICROSOFT)
> #include <malloc.h>
> #define alloca _alloca
> #elif defined(_AIX)
> #pragma alloca /* AIX requires this to be the first thing in the file. */
> #elif !defined(NO_ALLOCA)
> extern_C void* alloca (int size); /* see MALLOC(3V) */
> #endif
> #endif
>
> of something even simpler?
Here's how you can find out:
1) The module description says:
Description:
Memory allocation on the stack, as an optional optimization.
It allows using the alloca() macro if and only if the autoconf tests define
HAVE_ALLOCA.
...
Include:
<alloca.h>
So this means you should be able to write
#include <alloca.h>
#if HAVE_ALLOCA
... use alloca(n) ...
#endif
If you are still unsure:
2) Look at the unit test modules/alloca-opt-tests. It mentions a file
tests/test-alloca-opt.c. When you look there, it indeed does
#include <alloca.h>
#if HAVE_ALLOCA
... use alloca(n) ...
#endif
So really this way of using alloca is tested.
3) Finally there is also documentation:
<http://www.gnu.org/software/gnulib/manual/html_node/alloca_002dopt.html>
Bruno
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