Re: using array of char pointers gives wrong results

Let me bring the bug fix again to the surface. Is anybody looking at this
fix?

On Tue, Apr 29, 2014 at 2:25 PM, Ashutosh Bapat <
ashutosh(dot)bapat(at)enterprisedb(dot)com> wrote:

> Hi,
> When array of char * is used as target for the FETCH statement returning
> more than one row, it tries to store all the result in the first element.
> PFA test_char_select.pgc, which fetches first 3 relnames from pg_class
> ordered by relname. The program prints following result
>
> steps to compile and build the program
> ecpg -c -I<ecpg_include_dir> test_char_select.pgc
> cc -I<pg installation include dir> -g -c -o test_char_select.o
> test_char_select.c
> cc -g test_char_select.o -L<pg installation lib dir> -lecpg -lpq
> -lpgtypes -o test_char_select
>
> output
> ./test_char_select
> relname=___pg_foreign_table_columns
> relname=
> relname=
>
> The first three relnames should have been
> postgres=# select relname from pg_class order by relname limit 3;
> relname
> ---------------------------
> _pg_foreign_data_wrappers
> _pg_foreign_servers
> _pg_foreign_table_columns
>
> It's obvious that the first element of the array is being overwritten with
> an offset of 1.
>
> This happens because, the array of char pointer is dumped as
> /* Fetch multiple columns into one structure. */
> { ECPGdo(__LINE__, 0, 1, NULL, 0, ECPGst_normal, "fetch 3 from cur1",
> ECPGt_EOIT,
> ECPGt_char,(strings),(long)0,(long)3,*(1)*sizeof(char)*,
> ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, ECPGt_EORT);
>
> Since the offset is 1, the next result overwrites the previous result
> except for the first byte.
>
> PFA patch ecpg_char_ptr_arr.patch to fix this issue. It has changes as
> follows
> 1. Dump array of char pointer with right offset i.e. sizeof(char *)
> 2. While reading array of char pointer in ecpg_do_prologue(), use the
> address instead of the value at that address
> 3. The pointer arithmetic should treat such variable as char **, instead
> of char *
>
> ECPG regression tests do not show any failures with this patch.
> --
> Best Wishes,
> Ashutosh Bapat
> EnterpriseDB Corporation
> The Postgres Database Company
>

--
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company