Example: my_plus _counter Definition

my_plus _counter definition

#include "extfnapiv3.h"
#include <stdlib.h>

//  A simple non-deterministic scalar UDF that adds
//  an internal integer usage counter to its integer
//  argument and then returns the resulting integer.
//
//  Here, the start function creates a little structure for
//  the counter, and then the finish function deallocates it.
//
//  Corresponding SQL declaration:
//
//          CREATE FUNCTION plus_counter(IN arg1 INT) 
//                      RETURNS INT
//                      NOT DETERMINISTIC
//                      RESPECT NULL VALUES
//                      EXTERNAL NAME 'my_plus_counter@libudfex'


typedef struct my_counter {
  a_sql_int32 _counter;
} my_counter;

#if defined __cplusplus
extern "C" {
#endif

static void my_plus_counter_start(a_v3_extfn_scalar_context *cntxt)
{
  my_counter *cptr = (my_counter *)cntxt->_user_data;
  //  If we have not already allocated the
  //  counter structure, then do so now
  if (!cptr) {
    cptr = (my_counter *)malloc(sizeof(my_counter));
    cntxt->_user_data = cptr;
  }
  cptr->_counter = 0;
}


static void my_plus_counter_finish(a_v3_extfn_scalar_context *cntxt)
{
  //  If we still have an allocated the
  //  counter structure, then free it now
  if (cntxt->_user_data) {
    free(cntxt->_user_data);
    cntxt->_user_data = 0;
  }
}


static void my_plus_counter_evaluate(a_v3_extfn_scalar_context *cntxt, 
                                     void *arg_handle)
{
  an_extfn_value  arg;
  an_extfn_value  outval;
  a_sql_int32 arg1, result;

  //  Increment the usage counter
  my_counter *cptr = (my_counter *)cntxt->_user_data;
  cptr->_counter += 1;

  //  Get the one argument
  (void) cntxt->get_value( arg_handle, 1, &arg );
  if (!arg.data) {
    // argument value was NULL;
    arg1 = 0;
  } else {
    arg1 = *((a_sql_int32 *)arg.data);
  }

  outval.type = DT_INT;
  outval.piece_len = sizeof(a_sql_int32);
  result = arg1 + cptr->_counter;
  outval.data = &result;
  cntxt->set_value( arg_handle, &outval, 0 );
}


static a_v3_extfn_scalar my_plus_counter_descriptor = 
    {   &my_plus_counter_start, 
        &my_plus_counter_finish,
        &my_plus_counter_evaluate,
        NULL,                   // Reserved - initialize to NULL
        NULL,                   // Reserved - initialize to NULL
        NULL,                   // Reserved - initialize to NULL
        NULL,                   // Reserved - initialize to NULL
        NULL,                   // Reserved - initialize to NULL
        NULL,                   // _for_server_internal_use
};


a_v3_extfn_scalar *my_plus_counter()
{
  return &my_plus_counter_descriptor;
}

#if defined __cplusplus
}
#endif