Parameter Types for C++ Routines and Structures

Applies to TestComplete 15.20, last modified on January 13, 2022

This topic illustrates how you can specify parameter and member types for C++ routines and structures when calling DLL functions from TestComplete tests. The complete explanation of specifying the types is included in the description of IDefineDLL.DefineProc.

Important Notes

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

  • The table below in the topic holds examples of data types used in Microsoft Visual C++ v. 6.0. The size of some types may differ from one compiler to another or even from one version of a compiler to another version of the same compiler. If you doubt of the type size, refer to the documentation of your compiler.

  • C++ compilers 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 bool member, you should specify its type as vt_b4 instead of vt_b1. TestComplete does not align structure members itself.

    By default, the compiler uses alignment for those structures that are defined by default, that is, without the use of the #pragma pack(...) 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).

  • The void * type is not a Variant-compatible type and it is not supported.

  • 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.

Parameter Types

The following table shows correspondences between Microsoft Visual C++ v. 6.0 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.

Type Constant
bool vt_b1
BSTR vt_bstr
BSTR * vt_byref | vt_bstr
Byte vt_ui1
Byte * vt_byref | vt_ui1
char vt_i1
char * vt_lpstr
-- or --
vt_byref | vt_i1
This type is supported for function parameters only. The char * result type is not supported.
CLSID vt_clsid
CLSID * vt_byref | vt_clsid
CY vt_cy
CY * vt_byref | vt_cy
DATE vt_date
DATE * vt_byref | vt_date
DECIMAL Not supported.
double vt_r8
double * vt_byref | vt_r8
float vt_r4
float * vt_byref | vt_r4
HRESULT vt_ui4 (HRESULT is not a Variant-compatible type. If the function to be called uses this type, declare it as vt_ui4, but not as vt_hresult).
HRESULT * vt_byref | vt_ui4 (HRESULT is not a Variable-compatible type. If the function to be called uses HRESULT *, declare it as vt_byref | vt_ui4, but not as vt_byref | vt_hresult).
HWND vt_ui4 (for 32-bit DLLs)
-- or --
vt_ui8 (for 64-bit DLLs)
HWND * vt_byref | vt_ui4 (for 32-bit DLLs)
-- or --
vt_byref | vt_ui8 (for 64-bit DLLs)
IDispatch * vt_dispatch
IDispatch ** vt_byref | vt_dispatch
int vt_int
int * vt_byref | vt_int
long vt_i4
long * vt_byref | vt_i4
long long vt_i8
long long * vt_byref | vt_i8
LPCSTR vt_lpstr
LPCSTR * vt_byref | vt_lpstr
LPCTSTR vt_lpstr (for ANSI)
-- or --
vt_lpwstr (for Unicode)
LPCTSTR * vt_byref | vt_lpstr (for ANSI)
-- or --
vt_byref | vt_lpwstr (for Unicode)
LPCWSTR vt_lpwstr
LPCWSTR * vt_byref | vt_lpwstr
LPSTR vt_lpstr
LPSTR * vt_byref | vt_lpstr
LPTSTR vt_lpstr (for ANSI)
-- or --
vt_lpwstr (for Unicode)
LPTSTR * vt_byref | vt_lpstr (for ANSI)
-- or --
vt_byref | vt_lpwstr (for Unicode)
LPWSTR vt_lpwstr
LPWSTR * vt_byref | vt_lpwstr
SCODE vt_error
short vt_i2
short * vt_byref | vt_i2
unsigned int vt_uint
unsigned int * vt_byref | vt_uint
unsigned long vt_ui4
unsigned long * vt_byref | vt_ui4
unsigned long long vt_ui8
unsigned long long * vt_byref | vt_ui8
unsigned short vt_ui2
unsigned short * vt_byref | vt_ui2
VARIANT vt_variant
VARIANT * vt_byref | vt_variant
VARIANT_BOOL vt_bool
VARIANT_BOOL * vt_byref | vt_bool
wchar_t vt_ui2
wchar_t * vt_byref | vt_ui2
-- or --
vt_lpwstr

See Also

Calling DLL Functions From Tests
Calling DLL Functions From Tests - Overview
Calling DLL Functions From Tests - Tutorial
Returning Interface References From DLL Functions

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