Обсуждение: Determining C type for a given OID

Hi all,<br /><br />I'm using the libpq `PQgetvalue` function to get<br />specific results from my datase.  Many of
these<br/>results are numeric types.  Is there an internal<br />function in libpq that will convert the returned<br
/>stringto an appropriate C-type based on the oid<br />values in src/include/catalog/pg_type.h?<br /><br />Many
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Graham Wilson wrote:
> Hi all,
> 
> I'm using the libpq `PQgetvalue` function to get
> specific results from my datase.  Many of these
> results are numeric types.  Is there an internal
> function in libpq that will convert the returned
> string to an appropriate C-type based on the oid
> values in src/include/catalog/pg_type.h?

Well, in most queries, the returned value is a C string that you have
to convert in the client.  I think ecpg handles such conversions
natively so you don't have to worry about them, and most of the
scripting languages handle a C string numeric value just like any other
value (they don't have data types).  It would be great if we could
assign it right to a double, but you can't.

You can make such assignments of float4 to float and float8 to double if
you use a binary cursor _and_ your client and server have the same
internal representation for such values. However, NUMERIC is stored
internally a binary-coded decimal-like format that isn't going to make
any sense to your client code at all.

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