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