Access array of timestamp from composite-type argument in Postgres C Function

Question

I have a user-defined type mytype :

CREATE TYPE mytype AS (
    timestamps timestamp[], 
    last integer
);

I want to access values in timestamps field using C function. Here is what I have written :

#include "postgres.h"
#include "fmgr.h"
#include "executor/executor.h"
#include "datatype/timestamp.h"


#ifdef PG_MODULE_MAGIC
PG_MODULE_MAGIC;
#endif

PG_FUNCTION_INFO_V1(testfunc);

Datum
testfunc(PG_FUNCTION_ARGS) {
    bool isnull;
    HeapTupleHeader  at = PG_GETARG_HEAPTUPLEHEADER(0);
    Datum dt = GetAttributeByName(at, "timestamps", &isnull);

    Timestamp ** tts = (Timestamp **) DatumGetPointer(dt);

    PG_RETURN_DATUM(**tts);
}

SQL reference :

CREATE OR REPLACE FUNCTION testfunc(mytype) RETURNS timestamp AS 'path/to/library.so', 'testfunc' LANGUAGE C STRICT;

Now I am getting garbage result when I am trying to test:

postgres=# SELECT testfunc('("{""2017-01-11 00:00:00"", NULL}", 10)');
        testfunc        
---------------------------
 2000-01-01 00:00:00.00001
(1 row)

Laurenz Albe · Accepted Answer · 2017-01-11 12:52:41Z

1

Look at the PostgreSQL source code to see how to handle array arguments.

Your code should look somewhat like this:

HeapTupleHeader at = PG_GETARG_HEAPTUPLEHEADER(0);
Datum dt = GetAttributeByName(at, "timestamps", &isnull);
ArrayType *ts = DatumGetArrayTypeP(dt);
Timestamp *timestamps = (Timestamp *) ARR_DATA_PTR(ts);

This is not complete; you might want to add checks for NULL, if the array has the expected number of dimensions and similar.

edited Jan 11, 2017 at 12:52

answered Jan 11, 2017 at 8:34

Laurenz Albe

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2 Comments

gnuger Over a year ago

This is not working, perhaps because it is expecting first argument to be timestamp[] type but actually is a composite-type argument mytype. Also this page says that for composite-type HeapTupleHeader should be used.

Laurenz Albe Over a year ago

Argh, I forgot that it is a user-defined type. I have fixed the answer.

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