<cFunctionName>
The name of the function executed by the callback. Only non-STATIC functions can be specified. If no function name is passed, the method :execute() of the DllCallback object is executed.
Method DllCallback():new() Foundation
Initializes a callback object.
Syntax
:new( [<cFunctionName>], [<nCallmode>] [, <nParameterType1>, ...] ) --> oDllCallback
Parameters
<nCallmode>
Specifies the calling convention used by the DLL function when executing the callback as well as the callback's return type. One of the following #define
constants from dll.ch must be assigned to <nCallMode> for specifying the calling convention:
Constants for the calling convention of callback functions
| Constant | Description |
|---|---|
| DLL_STDCALL *) | Standard for Windows 32bit API |
| DLL_CDECL | C calling convention |
|
|
The return type of the DLL callback function can optionally be specified using the following #define constants. The contanst must be added to the calling
convention with the '+' operator.
Constants for the return type of callback functions
| Constant | Description |
|---|---|
| DLL_TYPE_INT16 | 16 bit unsigned integer |
| DLL_TYPE_UINT16 | 16 bit signed integer |
| DLL_TYPE_INT32 | 32 bit signed integer |
| DLL_TYPE_UINT32 *) | 32 bit unsigned integer |
| DLL_TYPE_INT64 | 64 bit signed integer |
| DLL_TYPE_UINT64 | 64 bit unsigned integer |
| DLL_TYPE_FLOAT32 | 32 bit floating point |
| DLL_TYPE_FLOAT64 | 64 bit floating point |
|
|
<nParameterType1>, ...
The data type of the parameter(s) of the callback function can optionally be defined via a list of data types starting with <nParameterType1>. A #define constant from the following table must be specified for each parameter that is expected by the callback function. The constants are defined
in the dll.ch include file.
Constants for the parameter type of callback functions
| Constant | Description |
|---|---|
| DLL_TYPE_INT16 | 16 bit unsigned integer |
| DLL_TYPE_UINT16 | 16 bit signed integer |
| DLL_TYPE_INT32 | 32 bit signed integer |
| DLL_TYPE_UINT32 | 32 bit unsigned integer |
| DLL_TYPE_INT64 | 64 bit signed integer |
| DLL_TYPE_UINT64 | 64 bit unsigned integer |
| DLL_TYPE_FLOAT32 | 32 bit floating point |
| DLL_TYPE_FLOAT64 | 64 bit floating point (double) |
| DLL_TYPE_STRING | Character string |
| DLL_TYPE_XPPVALUE | Xbase++ native value |
Return
The class method :new() returns a DllCallback object.
Description
Objects of the class DllCallback are used with DLL functions which execute a callback as a part of their operation. The method :new() establishes a reference to the Xbase++ code which is to be executed in the callback. The code may either be located in a separate function, or it must be implemented in the :execute() method of a user-defined callback class derived from DllCallback. :new() also sets information such as the calling convention which is required for executing the callback function, and for processing its parameters.
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