Re: PQSQL - binary data question

On 29. okt 2004, at 14:09, Bastian Voigt wrote:
> I just found this old posting on google. Now my question is how can I
> read an
> integer value from the PGresult using the binary format? Can someone
> plz
> gimme a code example? (please mail to me, because I have not
> subscribed to
> the list)

Easy peasy:

/* (in C++, actually would give simpler code in C) */

// To submit the query
bool PgConn::SendPrepared(const string& name, const vector<const
char*>& values, const vector<int>& lengths, const vector<int>&
isBinary) {
    if (values.size() != lengths.size() || values.size() !=
isBinary.size())
        return Error("PgConn::SendPrepared: All parameter arrays must have
same size");

//    for (int i = 0; i != values.size(); i++)
//        printf ("Query parameter %d, length %d, binary %d: '%s'\n", i,
lengths[i], (int)isBinary[i], values[i]);

    if (! PQsendQueryPrepared(m_Conn, name.c_str(), values.size(),
&values.front(), &lengths.front(), &isBinary.front(), 1 /* want binary
result */))
        return Error();

    return Success();
}


/* ... then after reading the PGresult */

static int NetworkIntFromBuffer(const char* buff) {
    // Make a network-byte-ordered integer from the fetched data
    const int *network = reinterpret_cast<const int*>(buff);
    // Convert to host (local) byte order and return
    int host = ntohl(*network);
    return host;
}
int PgColumn::GetInt(int row) {
    if (IsNull(row) || row > Rows() || GetLength(row) != 4)
        return 0;

    return NetworkIntFromBuffer(PQgetvalue(m_Res, row, m_Col));
}

> Thanks a bunch! Now here's the old posting:
>
> On Monday 27 October 2003 09:15, Tomasz Myrta wrote:
>> Dnia 2003-10-27 00:08, UÅytkownik creid napisaÅ:
>>> Problem:  Assigning a COUNT(*) result into an integer variable in my
>>> C
>>> program consistently fails except when I assign the same result to a
>>> char
>>> variable.  I can only assume that the internal data type the COUNT
>>> function uses is integer.
>>>
>>> Can anyone help put me in the proper mindset so I may deal with this,
>>> seemingly simple issue, to resolution.
>>>
>>> I need the integer result to to help me satisfy a dynamic memory
>>> requirement... COUNT(*) result will tell me how many rows of data I
>>> need
>>> to malloc and I cannot perform a math operation on a char variable.
>>
>> All libpq results are strings.
>> some_int_value=atoi(PQgetvalue(...))
>
> Not true anymore with protocol v3, which added the binary format. Text
> format
> is still the default.
>
>> Anyway why do you need count(*) ? When you retrieve your rows, you can
>> always check how many are them using PQntuples(...) and then malloc
>> your
>> memory tables.
>>
>> Regards,
>> Tomasz Myrta
>
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