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COM InteropC# supports calling unmanaged code. In this very short tutorial we will build a C++ unmanaged ATL COM dll and call it from C# using COM Interop. If you want to call a Win32 function, use PInvoke. Creating the C++ COM dll1) First create a C++ ATL project using Visual Studio 2003. File --> New --> Project --> Visual C++ --> ATL Project called TestATLCOM. 2) Add a simple COM class to the project. Project --> Add Class --> C++ --> ATL Simple Object and name it Test. 3) In the Class View right right click over ITest --> Add --> Add Method. Name the new method GetNumTokens. Add an in parameter of type BSTR called newValue. Add an in parameter of type long* called pValue. Click finish. 4) Modify the code in Test.h by changing the [in] parameter pValue to an [out, retval] parameter. The modified IDL should look like this:
Add the stl string library by adding an #include <string> directive like this:
// Test.h : Declaration of the CTest 5) Modify the Test.cpp code by adding a using namespace std statement like this: // Test.cpp : Implementation of CTest
You can now add the following implementation of GetNumTokens: // CTest STDMETHODIMP CTest::GetNumTokens(BSTR newValue, LONG* pValue)
{
// TODO: Add your implementation code here
CComBSTR bStr(""); // default empty string, remember NULL --> empty string
if (newValue != NULL) {
bStr= newValue; // you must copy a BSTR passed by value as [in} BSTR newValue
}
long lTokens= 0;
char cDelim= ',';
wstring strToken;
wstring inString(bStr);
wstring::size_type iPos;
iPos= inString.find(cDelim,0);
if (iPos == wstring::npos && inString.length() <= 0) { // no tokens
lTokens= 0;
strToken= L"";
}
else if (iPos== wstring::npos && inString.length() > 0) { // one token
lTokens = 1;
strToken= inString;
}
else { // more than one token
while (iPos != wstring::npos ) {
lTokens+= 1;
strToken= inString.substr(0,iPos);
inString= inString.substr(iPos+1);
iPos= inString.find(cDelim,0);
}
strToken= inString; // last token
lTokens+= 1;
}
*pValue= lTokens;
return S_OK;
}
6) Compile the project and Visual Studio will register the dll as TestCOMInterop 1.0 Type Library. Thats it. Calling COM dllTo call our COM dll, just create a C# console application and add a reference to our TestCOMInterop dll. 1) Create a new C# console application called CallATLCOM. 2) Add a reference to our TestCOMInterop dll. Project --> Add Reference... --> COM --> TestCOMInterop 1.0 Type Lib... --> Select --> OK. This auto magically wraps the unmanaged C++ code into a managed class. You can also do this from the command line using TlbImp.exe, the Type Library Importer. Here is the assembler code that calls the unmanaged code: .method public hidebysig newslot virtual
instance int32 GetNumTokens([in] string
marshal( bstr) newValue) runtime
managed internalcall
{
.custom instance void [mscorlib]System.Runtime.InteropServices.DispIdAttribute::.ctor(int32) =
( 01 00 01 00 00 00 00 00 )
.override TestCOMInterop.ITest::GetNumTokens
} // end of method CTestClass::GetNumTokens
3) Now just call our Test method by passing a comma delimited string. The Test method simply returns the number of tokens in the string. Here is the CallATLCOM source code: namespace CallATLCOM
{
/// <summary>
/// Summary description for Class1.
/// </summary>
class Class1
{
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main(string[] args)
{
//
// TODO: Add code to start application here
//
TestCOMInterop.CTestClass o= new TestCOMInterop.CTestClass();
System.Console.WriteLine(o.GetNumTokens("Hello,World"));
System.Console.ReadLine();
}
}
}
Output: 2 Learn MoreHere are some links that may be helpful:
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