Thread: [GENERAL] Receive a string in Composite-type Arguments

[GENERAL] Receive a string in Composite-type Arguments

From

Fabiana Zioti

Date:

11 August 2017, 19:09:13

Hi!

I am studying how to program extensions for PostgreSQL in C language.

In the example to return to return Composite-type Arguments, from the PostgreSQL 9.6 documentation, I could not make the cash from a cstring to the HeapTupleHeader type.

That is, instead of the function receive as a parameter a table:

CREATE FUNCTION c_overpaid (emp, integer) RETURNS boolean
AS DIRECTORY

SELECT name, c_overpaid (emp, 1500) AS overpaid
     From emp
     WHERE name = 'Bill' OR name = 'Sam';

And in the code in C receive the argument as:

HeapTupleHeader t = PG_GETARG_HEAPTUPLEHEADER (0);

The sql function would be defined as:

CREATE FUNCTION c_overpaid (cstring, integer) RETURNS boolean
     AS 'DIRECTORY / funcs', 'c_overpaid'
     LANGUAGE C STRICT;

But how would I receive this argument, for example:
Char * str = PG_GETARG_CSTRING (0),

And do the conversion to the HeapTupleHeader type?

What do you guys suggest?

Thanks in advance

Re: [GENERAL] Receive a string in Composite-type Arguments

From

Achilleas Mantzios

Date:

11 August 2017, 20:39:24

On 11/08/2017 16:09, Fabiana Zioti wrote:

Hi!

I am studying how to program extensions for PostgreSQL in C language.

In the example to return to return Composite-type Arguments, from the PostgreSQL 9.6 documentation, I could not make the cash from a cstring to the HeapTupleHeader type.

That is, instead of the function receive as a parameter a table:

CREATE FUNCTION c_overpaid (emp, integer) RETURNS boolean
AS DIRECTORY

SELECT name, c_overpaid (emp, 1500) AS overpaid
     From emp
     WHERE name = 'Bill' OR name = 'Sam';

And in the code in C receive the argument as:

HeapTupleHeader t = PG_GETARG_HEAPTUPLEHEADER (0);

The sql function would be defined as:

CREATE FUNCTION c_overpaid (cstring, integer) RETURNS boolean
     AS 'DIRECTORY / funcs', 'c_overpaid'
     LANGUAGE C STRICT;

But how would I receive this argument, for example:
Char * str = PG_GETARG_CSTRING (0),

And do the conversion to the HeapTupleHeader type?

Why do you want to convert this to HeapTupleHeader since this is *not* a tuple but a string value? What do you want to achieve? IMHO you better start with simpler examples, make them run, and proceed as you understand more and more.

What do you guys suggest?

Thanks in advance

-- 
Achilleas Mantzios
IT DEV Lead
IT DEPT
Dynacom Tankers Mgmt

Re: [GENERAL] Receive a string in Composite-type Arguments

From

Pavel Stehule

Date:

11 August 2017, 21:12:27

2017-08-11 16:39 GMT+02:00 Achilleas Mantzios <achill@matrix.gatewaynet.com>:

On 11/08/2017 16:09, Fabiana Zioti wrote:
Hi!

I am studying how to program extensions for PostgreSQL in C language.

In the example to return to return Composite-type Arguments, from the PostgreSQL 9.6 documentation, I could not make the cash from a cstring to the HeapTupleHeader type.

That is, instead of the function receive as a parameter a table:

CREATE FUNCTION c_overpaid (emp, integer) RETURNS boolean
AS DIRECTORY

SELECT name, c_overpaid (emp, 1500) AS overpaid
     From emp
     WHERE name = 'Bill' OR name = 'Sam';

And in the code in C receive the argument as:

HeapTupleHeader t = PG_GETARG_HEAPTUPLEHEADER (0);

The sql function would be defined as:

CREATE FUNCTION c_overpaid (cstring, integer) RETURNS boolean
     AS 'DIRECTORY / funcs', 'c_overpaid'
     LANGUAGE C STRICT;

But how would I receive this argument, for example:
Char * str = PG_GETARG_CSTRING (0),

And do the conversion to the HeapTupleHeader type?

you have to build tuple first. Later you can got a HeapTupleHeader

pl_toolbox has some functions for composite types

https://github.com/okbob/pltoolbox

Regards

Pavel Stehule

Why do you want to convert this to HeapTupleHeader since this is *not* a tuple but a string value? What do you want to achieve? IMHO you better start with simpler examples, make them run, and proceed as you understand more and more.

What do you guys suggest?

Thanks in advance

-- Achilleas Mantzios IT DEV Lead IT DEPT Dynacom Tankers Mgmt