External functions

An external function is an object of the D2000 system, that allows extending the standard set of functions that are comprised in the mathematical apparatus. The External function object represents an exported function in a dynamically linked library (file). When properly implemented, they allow to substitute (in some cases also simplify) system extensions implemented by the interfaces D2000 ObjApi or D2000 KomAPI.

The creation of an External function consists of two steps:

• Implementation of a function within a dynamically linked library,
• Definition of an object of External function type.

Function Implementation

External functions for the D2000 system can be written in C ++ language and the D2ExtFunc library must be used for their implementation. Also included is an example of the external function library  (utils/d2extfunc/sample directory in the D2000 installation directory), which also provides the following example of an external function implementation.

int DemoRedim(SyncRoutedFunctionParams& params) {
	// Parameter check: the first parameter must be the structure, the second simple integer 
	if (params.getCount() != 2
		|| !params[0].isStructured()
		|| !params[1].isSimple() || params[1].getType() != Integer)
		return CallError; // Wrong number or types of parameters - generates runtime exception in ESL

	// If the parameter specifying the new dimension of the structure is valid, 
	if (params[1].isValid()) {
		// then it will change the structure dimension
		params[0].setRowsCount(params[1].getValueInteger());
		for (int i = 1; i < params[0].getRowsCount(); ++i) {
			// and copy the values from the first row into the other ones
			for (int j = 0; j < params[0].getColumnsCount(); ++j) {
				params[0].copyValue(params[0], 0, j, i, j);
			}
		}
	}
	// Calling of the external function was successful 
	return CallSuccess;
}

Errors and exceptions handling

Performing external functions takes place in the same environment as running the ESL scripts that call them. If the implementation of an external function ends with a catchable C ++ exception, this exception is caught and promoted as a runtime error to the ESL. However, some C ++ errors (e. g., NULL dereference, division 0) do not generate catchable exceptions and end up with the fallout of the library and the process used by the library (Event handler), so it is important to care thoroughly of handling errors when implementing external functions.

Example of calling an external function

BEGIN
  RECORD NOALIAS (SD.ExtFunc) _rec
  CALL %DemoRedim(_rec, 10)
END