PostgreSQL: How to get parameters in C extension function?

Question

I'm writing a C user defined extension function for Postgres and would like to get the value of parameter that I set in SQL level in my C code.

For example, in SQL, I have something like:

CREATE FUNCTION my_test_function(text) RETURNS text AS 'path_to_so', 'my_function' LANGUAGE C STRICT SET some_boolean TO true;

The question is how can I get the value of some_boolean variable in my C code?

Datum my_test_function(PG_FUNCTION_ARGS) {
// try to get some_boolean here
}

Laurenz Albe · Accepted Answer · 2018-01-22 18:35:36Z

1

some_boolean must be an existing GUC (configuration parameter), else the function definition will produce

ERROR:  unrecognized configuration parameter "some_boolean"

If it is a GUC, it is either a core PostgreSQL GUG, or it was registered somewhere with DefineCustomBoolVariable (from utils/guc.h).

Each GUC belongs to a C variable, commonly a global one.

Use that variable in your code!

answered Jan 22, 2018 at 18:35

Laurenz Albe

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1 Comment

Thank @Laurenz Albe. It's registered in _PG_init function.