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Date: Mon, 3 Dec 2012 08:42:48 -0600
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 <CAHyXU0wSbZp3gdtm__LU+rGYs4JxdM84o+1rx=ytyYayymP_2Q@mail.gmail.com>
Subject: Re: Exception Handling in C-Language Functions?
From: Merlin Moncure <mmoncure@gmail.com>
To: rahul143 <rk204885@gmail.com>
Cc: pgsql-general@postgresql.org
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On Sun, Dec 2, 2012 at 11:18 PM, rahul143 <rk204885@gmail.com> wrote:
> I have the created a C-Language function (code is below).  Now, I
> wonder: How do I handle exceptions, for example if malloc cannot assign
> the necessary memory?  Do "palloc" and "pfree" handle such a case
> cleanly?  Should I simply use an "assert"?
>
> #include "postgres.h"
> #include <string.h>
> #include <stdlib.h>
> #include "fmgr.h"
> #include "libinn.h"
>
> PG_FUNCTION_INFO_V1(ffiinews_uwildmat);
>
> /* Wrapper for INN's function uwildmat.  Needs parameters in UTF-8. */
> Datum ffiinews_uwildmat(PG_FUNCTION_ARGS) {
>     VarChar *text = PG_GETARG_VARCHAR_P(0);
>     VarChar *pattern = PG_GETARG_VARCHAR_P(1);
>     int text_len = VARSIZE(text)-VARHDRSZ;
>     int pattern_len = VARSIZE(pattern)-VARHDRSZ;
>     char *tmp_text = (char *)malloc(text_len+1);
>     if (tmp_text == NULL)
>         ; /* What now? */
>     char *tmp_pattern = (char *)malloc(pattern_len+1);
>     if (tmp_pattern == NULL)
>         ; /* What now? */
>     strncpy(tmp_text, VARDATA(text), text_len);
>     tmp_text[text_len] = '\0';
>     strncpy(tmp_pattern, VARDATA(pattern), pattern_len);
>     tmp_pattern[pattern_len] = '\0';
>     bool matches = uwildmat(tmp_text, tmp_pattern);

yes, you should always use database memory api: palloc/pfree and if
necessary memory context switching.  memory allocation error then
raises database exception.  any situation that raises an exception or
other critical needs to be caught and rethrown as database exception
(ereport, etc).

merlin


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