How to obtain the size of a field VARCHAR, NUMERIC(7, 2) after a query with libpq?

From: Gilberto Ribeiro de Queiroz <gribeiro(at)dpi(dot)inpe(dot)br>
To: pgsql-interfaces(at)postgresql(dot)org
Subject: How to obtain the size of a field VARCHAR, NUMERIC(7, 2) after a query with libpq?
Date: 2001-10-27 20:30:33
Message-ID: 1004214633.3bdb1969d53e5@lagavulin.ltid.inpe.br
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I am using the library C of the PostgreSQL "libpq" in some academic projects. I
am needing to recover the size of the resulting fields of a given
query so that, if necessary, I create a new table in another database or so that
my program has this information for posterior use.

Below, it is an example that I want to do

Given the tables:
T1(C1 VARCHAR(89), C2 NUMERIC(7,2))
T2(C2 NUMERIC(7,2))

1 - the user executes a consultation like:
SELECT C1 FROM T1, T2 WHERE T1.C2 = T2.C2 ORDER BY C1

2 - later he (or she) decides, inside of my program, to export the result for a
table of another database (like MySQL for example) => Then, I will have to know
the type (this libpq gives) and the size of each field so that I can create a
table in MySQL, in the case of this example, I will have to discover that the
field C1 of the table T1 is a varchar of length "89".

===> How could I get this length ?

Since now i thanks everybody, Gilberto.

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