Re: using arrays within structure in ECPG

2014-03-24 07:22 keltezéssel, Ashutosh Bapat írta:
> Hi,
> I tried using integer array within a structure array in ECPG code. But it resulted in
> some garbage values being printed from the table. Here are the details,
>
> The ECPG program is attached (array_test.pgc). It tries to read the contents of table
> emp, whose structure and contents are as follows
> postgres=# \d+ emp
> Table "public.emp"
> Column | Type | Modifiers | Storage | Stats target | Description
> ---------+-------------------+-----------+----------+--------------+-------------
> empno | numeric(4,0) | | main | |
> ename | character varying | | extended | |
> job | character varying | | extended | |
> arr_col | integer[] | | extended | |
> Has OIDs: no
>
> postgres=# select * from emp;
> empno | ename | job | arr_col
> -------+--------+---------+------------
> 7900 | JAMES | CLERK | {1,2,7900}
> 7902 | FORD | ANALYST | {1,2,7902}
> 7934 | MILLER | CLERK | {1,2,7934}
> (3 rows)
>
> You will notice that the last element of the arr_col array is same as the empno of that
> row.
>
> The ECPG program tries to read the rows using FETCH in a structure emp defined as
> 15 struct employee {
> 16 int empno;
> 17 char ename[11];
> 18 char job[15];
> 19 int arr_col[3];
> 20 };
>
> and then print the read contents as
> 39 /* Print members of the structure. */
> 40 for ( i = 0 ;i < 3; i++){
> 41 printf("empno=%d, ename=%s, job=%s, arr_col[2]=%d\n", emp[i].empno,
> emp[i].ename, emp[i].job, emp[i].arr_col[2]);
> 42
> 43 }
>
> But garbage values are printed
> [ashutosh(at)ubuntu repro]./array_test
>
> +++++++++++++++++++++++++++++++++++++++++++++++
> empno=7900, ename=JAMES, job=CLERK, arr_col[2]=1
> empno=2, ename=�, job=ANALYST, arr_col[2]=32767
> empno=7934, ename=MILLER, job=CLERK, arr_col[2]=1719202336
>
> Here are steps I have used to compile the ECPG program
> [ashutosh(at)ubuntu repro]make array_test
> ecpg -c -I/work/pg_head/build/include array_test.pgc
> cc -I/work/pg_head/build/include -g -c -o array_test.o array_test.c
> cc -g array_test.o -L/work/pg_head/build/lib -lecpg -lpq -o array_test
> rm array_test.o array_test.c
>
> where /work/pg_head/build is the directory containing the postgresql build (essentially
> argument to the --prefix option to configure).
>
> The programs compiles and links fine.
>
> Without the arr_col member, the program works fine. So, it seems to be a problem with
> array within structure array.
>
> In array_test.c I see that the ECPGdo statement corresponding to the FETCH command is as
> follows
> 87 /* Fetch multiple columns into one structure. */
> 88 { ECPGdo(__LINE__, 0, 1, NULL, 0, ECPGst_normal, "fetch 3 from cur1", ECPGt_EOIT,
> 89 ECPGt_int,&(emp->empno),(long)1,(long)14,sizeof( struct employee ),
> 90 ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L,
> 91 ECPGt_char,&(emp->ename),(long)11,(long)14,sizeof( struct employee ),
> 92 ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L,
> 93 ECPGt_char,&(emp->job),(long)15,(long)14,sizeof( struct employee ),
> 94 ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L,
> 95 ECPGt_int,(emp->arr_col),(long)1,(long)3,sizeof(int),
> 96 ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, ECPGt_EORT);
>
> For all the members of struct employee, except arr_col, the size of array is set to 14
> and next member offset is set of sizeof (struct employee). But for arr_col they are set
> to 3 and sizeof(int) resp. So, for the next row onwards, the calculated offset of
> arr_col member would not coincide with the real arr_col member's address.
>
> Am I missing something here?

ECPG (I think intentionally) doesn't interpret or parse array fields.
You need to pass a character array and parse the contents by yourself.

Best regards,
Zoltán Böszörményi

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