Parameter Types for Delphi Routines and Structures

Important Notes

Parameter Types

When specifying parameter and member types for Delphi routines and structures located in DLLs, keep in mind the following specifics:

• Delphi compiler can align structure members at certain bounds: at bytes, words, double words, etc. For instance, applications often use double word alignment. In this case the address of each member is a multiple of 4. So, if a structure has a Boolean member, you should specify its type as vt_b4 instead of vt_b1.

  By default, the compiler uses alignment for those structures that are defined by default, that is, without the use of the packed record statement. So, when creating a data type for the “default” structures in scripts, pay attention to the size of the structure members.

• Make sure you specified the parameter types correctly. Defining the parameter types incorrectly may cause TestComplete to shut down (this happens because erroneous definitions cause incorrect stack processing).

• For JavaScript, JScript, Python, C#Script and C++Script users: These scripting languages do not support passing variables by references through parameters of a function being called. Therefore, you cannot pass a variable of an ordinary data type (like integer, boolean, etc.) by a reference to a DLL routine and get the value modified by the routine in your JavaScript, JScript, Python, C#Script or C++Script (this restriction applies to C#Script and C++Script too since these languages are based on JScript and use the JScript engine) test. In this case, the value of the variable passed to the DLL routine from your JavaScript, JScript, Python, C#Script or C++Script test actually remains the same after the routine execution is over because the routine works with a copy of the variable.

  However, objects are passed through routine parameters by references in these languages, and if the callee routine modifies some members of an object passed through its parameters, the caller routine can access the updated object. Therefore, if you pass a custom structure, array or string value created by the DLL.New or IDLLAccessProcess.New method (see Using Custom Data Structures in DLL Function Calls, Using Arrays in DLL Function Calls and Using String Parameters in DLL Function Calls) from your JavaScript, JScript, Python, C#Script or C++Script test to a DLL routine, you can then access the modified structure, array or string after the routine execution is over. The point is that such structures, arrays and strings are created by the New methods as wrapper objects and such objects passed to a DLL routine can be modified and returned from the routine to which they are passed by references.

• In Python, all constants are capitalized. So, you write VT_BYREF, VT_R4 and so on.

The following table shows correspondences between Delphi data types and special constants used in TestComplete when calling the IDefineDLL.DefineProc, DLL.DefineType and IDLLAccessProcess.DefineType methods to specify data types of DLL functions’ parameters or members of structures defined in DLLs.