Postgresql PQgetvalue: array return

Question

I've a table created like:

CREATE TABLE tbl_test
(
  id        bigserial    PRIMARY KEY,
  interest  int          ARRAY[2]
);

I got PGresult* res using PQexec(conn, "SELECT * FROM tbl_test");

Now, how can I get int[] from PQgetvalue(res, 0, 1).
I don't want to depend on structs defined in array.h as they might change.

I could not find any API in Postgresql docs which can do things.
Please advise.

Regards,
Mayank

You've specified what return type you want; but please update the question to be explicit about what return value you want. — bignose
– bignose, Commented May 15, 2011 at 9:30

Mike Sherrill 'Cat Recall' · Accepted Answer · 2011-05-15 12:09:42Z

7

+50

PQgetvalue() returns the string representation of the field value unless you specify a binary cursor. In either case (string or binary cursor) you'll need to supply the code to manipulate the result into the form you want.

You might find some ideas in the PostgreSQL source code.

src/backend/utils/adt/arrayfuncs.c
src/include/utils/array.h.

And there's some code in contrib/intarray.

At http://doxygen.postgresql.org/, click "Files", then search for "array".

At the string level, which is what PQgetvalue() returns, it's probably easy to Google up some code that extracts integers from an comma-delimited string.

edited May 15, 2011 at 12:09

answered May 15, 2011 at 9:08

Mike Sherrill 'Cat Recall'

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3 Comments

Mayank Over a year ago

Looks like its not possible what I need :)

Mike Sherrill 'Cat Recall' Over a year ago

Oh, it's possible. There's just not an API for it. You can write a function in C that accepts a string, like "{1,2,3}", and returns (or populates) an array of int. It's not dead simple, because you'd have to accommodate (or give up on) multi-dimensional arrays and arrays of arbitrary size. But it's possible. I knocked together some code to turn "{1,2,3}" into an array of int, and it wasn't too hard. (I learned to hate strtol(), though.)

Mayank Over a year ago

Thanks a lot Catcall. I meant its not possible to get int* in return. Converting {x,y} is a different thing. Well, I'll be doing that :)

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