Example: my_byte_length Definition

#include "extfnapiv4.h"
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <assert.h>


//  A simple function that returns the size of a cell value in bytes
//
//	CREATE FUNCTION my_byte_length(IN arg1 LONG BINARY) 
//			RETURNS UNSIGNED INT
//			DETERMINISTIC
//          IGNORE NULL VALUES
//			EXTERNAL NAME 'my_byte_length@libudfex'

#if defined __cplusplus
extern "C" {
#endif

static void my_byte_length_evaluate(a_v3_extfn_scalar_context *cntxt, 
                      void *arg_handle)
{

	if (cntxt == NULL || arg_handle == NULL) 
	{
		return;
	}
	
    an_extfn_value  arg;
    an_extfn_value  outval;

    a_sql_uint64 total_len;

    //  Get first argument
    a_sql_uint32 fetchedLength = 0;
    (void) cntxt->get_value( arg_handle, 1, &arg );
    if (arg.data == NULL)
    {
        return;
    }

    fetchedLength += arg.piece_len;

    // saving total length as it loses scope inside get_piece
    total_len = arg.len.total_len;

    while (fetchedLength < total_len)
    {
        (void) cntxt->get_piece( arg_handle, 1, &arg, fetchedLength );
        fetchedLength += arg.piece_len;
    }

	//if this fails, the function did not get the full data from the cell
	assert(fetchedLength == total_len);
	
	outval.type = DT_UNSINT;
	outval.piece_len = 4;
	outval.data = &fetchedLength;
	cntxt->set_value(arg_handle, &outval, 0);
}

static a_v3_extfn_scalar my_byte_length_descriptor = { 
    0, 
    0, 
    &my_byte_length_evaluate,
    0,          // Reserved - initialize to NULL
    0,          // Reserved - initialize to NULL
    0,          // Reserved - initialize to NULL
    0,          // Reserved - initialize to NULL
    0,          // Reserved - initialize to NULL
        NULL                    // _for_server_internal_use
};

a_v3_extfn_scalar *my_byte_length()
{
  return &my_byte_length_descriptor;
}

#if defined __cplusplus
}
#endif