Solution
TestStand must obtain function prototype information to populate the parameter table. TestStand can automatically retrieve this information only if the DLL provides recognizable metadata.
The C/C++ DLL Adapter extracts parameter information using:
- Decorated (mangled) C++ export names generated by Visual Studio, which encode parameter types and calling convention.
- Prototype information embedded in DLLs built with LabWindows/CVI, which TestStand can read without requiring a standard COM type library.
If none of these sources are available, the DLL appears to TestStand as lacking parameter information.
This situation commonly occurs when:
- The DLL is a C DLL built in Microsoft Visual Studio, which exports only bare function names and contains no prototype metadata
- The DLL is a C++ DLL exported with
extern "C", which removes decorated names and therefore removes the encoded parameter information normally present in C++ exports - The DLL uses data types that are not supported by the C/C++ DLL Adapter
- The DLL does not contain a type library and no source file is provided for TestStand to parse
Use one of the following supported mechanisms to provide prototype information to TestStand:
C++ DLLs (Microsoft Visual Studio)
Export functions using standard C++ linkage so that the compiler generates decorated names (name mangling). TestStand can decode these names to determine parameter types and calling conventions.
Recommended:
__declspec(dllexport) int Add(int a, int b);
Avoid:
extern "C" __declspec(dllexport) int Add(int a, int b);
Using extern "C" suppresses name decoration and prevents the C/C++ DLL Adapter from obtaining parameter information from export names.
Refer to the Exporting Class Methods and Functions in Microsoft Visual Studio page in the TestStand Help for further information.
C DLLs (Microsoft Visual Studio)
Standard C DLLs export only function names and do not include parameter metadata. To use these DLLs with TestStand:
- Associate a
.c or .cpp file that contains the function prototype with the step
-
In the Module tab of the Step Settings Pane, click the Verify Prototype button
-
Search for the source code file and click OK.
- Manually configure the function parameters in the Module tab
Because C DLLs do not encode prototype information in exported symbols, TestStand cannot infer parameters automatically.
LabWindows™/CVI™ DLLs
DLLs built with LabWindows™/CVI™ 7.1 or later include embedded prototype information that TestStand can read directly, even for C functions that use enums, structs, or typedefs.
Ensure that:
- Type Information is enabled in the CVI project
- Only the desired symbols are marked for export
This is the recommended method for C‑based DLLs that need automatic parameter inference in TestStand.
Refer to the Create and build the LabWindows™/CVI™ DLL section of the Using LabWindows™/CVI™ Enums in TestStand Knowledgebase article to learn how to setup a CVI DLL so that TestStand can parse the function parameters, even when using the C/C++ Adapter.
Supported Data Types
The C/C++ DLL Adapter supports only parameter and return types that can be mapped to TestStand data types. According to the Parsing Parameters from Source Code help page:
- Parameters must be numeric, arrays, strings, or object‑type pointers.
- Return values must be numeric or void.