Problem with using snprintf in C-function

2009/10/17 Ilya Urikh <ilya.urikh@gmail.com>:

Hi,

I have a problem with snprintf function which insert the variables to string
with error.
This code I wrote for PostgreSQL 8.3.7 on Fedora 10 and it worked fine. But
now I use CentOS 5.3 and PostgreSQL 8.3.8.

Function:
Datum calculateAccount(PG_FUNCTION_ARGS) {
    int64   accountId = PG_GETARG_INT64(0);
    DateADT startDate = PG_GETARG_DATEADT(1);
    DateADT endDate = PG_GETARG_DATEADT(2);

    char    command[QUERY_MAX_SIZE];
    char    startDateStr[MAXDATELEN + 3];
    char    endDateStr[MAXDATELEN + 3];

    snprintf(startDateStr, sizeof (startDateStr), "'%s'",
DatumGetCString(DirectFunctionCall1(date_out, startDate)));
    snprintf(endDateStr, sizeof (endDateStr), "'%s'",
DatumGetCString(DirectFunctionCall1(date_out, endDate)));
    elog(INFO, startDateStr);
    elog(INFO, endDateStr);
    snprintf(command, sizeof (command),
            "SELECT serviceId, periodStartDate, periodEndDate\
             FROM   accountServiceBaseView\
             WHERE  accountId = %ld AND\
                    periodStartDate <= %s AND\
                    periodEndDate >= %s;",
            accountId, startDateStr, endDateStr);
    elog(INFO, command);

Hello

my reply is little bit offtopic. Why you convert date values to
string? You can use placeholders and execute query with parameters in
native format. It's more simply and safe.

Regards
Pavel Stehule

Pavel,

Could you provide some example? I don't really understand which placeholder
I can use.

On Sun, Oct 18, 2009 at 1:20 AM, Pavel Stehule <pavel.stehule@gmail.com>wrote:

2009/10/17 Ilya Urikh <ilya.urikh@gmail.com>:

Hi,

I have a problem with snprintf function which insert the variables to

string

with error.
This code I wrote for PostgreSQL 8.3.7 on Fedora 10 and it worked fine.

But

now I use CentOS 5.3 and PostgreSQL 8.3.8.

Function:
Datum calculateAccount(PG_FUNCTION_ARGS) {
int64 accountId = PG_GETARG_INT64(0);
DateADT startDate = PG_GETARG_DATEADT(1);
DateADT endDate = PG_GETARG_DATEADT(2);

char command[QUERY_MAX_SIZE];
char startDateStr[MAXDATELEN + 3];
char endDateStr[MAXDATELEN + 3];

snprintf(startDateStr, sizeof (startDateStr), "'%s'",
DatumGetCString(DirectFunctionCall1(date_out, startDate)));
snprintf(endDateStr, sizeof (endDateStr), "'%s'",
DatumGetCString(DirectFunctionCall1(date_out, endDate)));
elog(INFO, startDateStr);
elog(INFO, endDateStr);
snprintf(command, sizeof (command),
"SELECT serviceId, periodStartDate, periodEndDate\
FROM accountServiceBaseView\
WHERE accountId = %ld AND\
periodStartDate <= %s AND\
periodEndDate >= %s;",
accountId, startDateStr, endDateStr);
elog(INFO, command);

Hello

my reply is little bit offtopic. Why you convert date values to
string? You can use placeholders and execute query with parameters in
native format. It's more simply and safe.

Regards
Pavel Stehule

PG_RETURN_BOOL(true);
}

Result:
select calculateaccount(123, '01-01-2009', '01-02-2009');
INFO: '2009-01-01'
INFO: '2009-02-01'
INFO: SELECT serviceId, periodStartDate, periodEndDate FROM
accountServiceBaseView WHERE accountId = 123 AND periodStartDate <=

(null)

AND periodEndDate >= '2009-01-01';

If I change the order of parameters to "periodStartDate <= %s AND
periodEndDate >= %s AND accountId = %ld", all works fine. Unfortunately

this

method can not be applied to other functions of my module.

--
Best regards,
Ilya Urikh.

--
Best regards,
Ilya Urikh.

2009/10/17 Ilya Urikh <ilya.urikh@gmail.com>:

Pavel,

Could you provide some example? I don't really understand which placeholder
I can use.

here is one fragment from orafce:
it's for delete statement, but SELECT statement is similar

ItemPointer tid;
Oid argtypes[1] = {TIDOID};
char nulls[1] = {' '};
Datum values[1];
void *plan;

tid = &rettuple->t_data->t_ctid;

if (!(plan = SPI_prepare("DELETE FROM ora_alerts WHERE ctid = $1",
1, argtypes)))
ereport(ERROR,
(errcode(ERRCODE_TRIGGERED_ACTION_EXCEPTION),
errmsg("SPI_prepare failed")));

values[0] = ItemPointerGetDatum(tid);

if (SPI_OK_DELETE != SPI_execute_plan(plan, values, nulls, false, 1))
ereport(ERROR,
(errcode(ERRCODE_TRIGGERED_ACTION_EXCEPTION),
errmsg("can't execute sql")));

SPI_finish();
return PointerGetDatum(rettuple);

I don't found better samples, but both functions are well documented.

your code should look like:

Datum params[3];
char nulls[3] = {' ',' ',' '} ;
Oid types[3] = {INT8OID, DATEOID, DATEOID};
void *plan;

params[0] = PG_GETARG_DATUM(0);
params[1] = PG_GETARG_DATUM(1);
params[2] = PG_GETARG_DATUM(2);

nulls[0] = PG_ARGISNULL(0) ? 'n' : ' ';
...

plan = SPI_prepare("SELECT ...",3, types);
if (plan == NULL)
... raise exception

result = SPI_execute_plan(plan, params, nulls, true, -1);
...

Regards
Pavel Stehule.

Ilya Urikh <ilya.urikh@gmail.com> writes:

This code I wrote for PostgreSQL 8.3.7 on Fedora 10 and it worked fine. But
now I use CentOS 5.3 and PostgreSQL 8.3.8.

It looks to me like you're assuming that %ld is the appropriate format
string for an int64 value. This might be true on a 64-bit machine but
it would not be on 32-bit. It's not obvious why that would lead to
exactly the results you show, but it could certainly account for
snprintf fetching the wrong bits for some of its arguments.

The portable way (within Postgres code) is to use INT64_FORMAT, which
will be set up correctly by configure. So instead of

WHERE accountId = %ld AND\

you need

WHERE accountId = " INT64_FORMAT " AND\

(relying on concatenation of literals in C).

BTW, if your compiler didn't warn you about this, you need to get a
new compiler, or at least start using the switches that would make it
warn you. If you did get a warning, and ignored it, you need to
learn better habits ;-)

regards, tom lane