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I have a C++ class and I want to import it into C#.

C++
class __declspec(dllimport) string
{
public:
	string();
	string(const char*);
	string(const std::string&);
	~string();
	int   size() const;
	int   lenth() const;
	const char* c_str() const;

	string& operator=(const char* str);
	string& operator=(const std::string& str);
private:
	char* _data;
	int _lenth;
};


What I have tried:

I've tried to convert it to C# but I couldn't find a way to DllImport a class and Operation overloading for '='?
I need an object from this class in my C# code. Is there any way to do this?
Posted
Updated 7-Feb-23 23:28pm
v2
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Richard MacCutchan 1-Jun-21 8:23am    
See Solution 2

I feel like this is a follow-up to the other question asked here[^], why didn't you just put a comment on that question?

As far as I'm aware you cannot share classes between C# and C++, it's just not a supported option. As I mentioned on the other question, you can use a char* if you need to pass string values between the two. From your original question I don't particularly see why it has to be an instance of your string class?

Otherwise, this StackOverflow question[^] highlights how you can export functions to create, call and drop a class instance. But using the interop services, this just isn't going to be possible.
 
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v2
Comments
mohammad hasani 1-Jun-21 8:35am    
Thank you for your response.
I'm using a DLL which is accepting an object of this class 'base::string'.
and I can't change the DLL to accept char* instead of base::string.
I'm importing the DLL in my C# code and I need to pass an object of base::string to the function otherwise It's going to throw an AccessViolation Exception.
The code above is the header for base::string which is implemented in the DLL.
Chris Copeland 1-Jun-21 10:46am    
Chris Losinger below provides a good compromise. If you absolutely cannot change the DLL then why not write an intermediary C++ DLL which has a method which does accept the char*? Then simply have that method forward the invoke onto the correct method after creating the base::string instance?
mohammad hasani 1-Jun-21 12:36pm    
Thank you I'll try that
You cannot import a C++ class into C#. The two languages are completely different and C++ runs under native Windows, while C# requires .NET.

C# programs can access C-style functions via Platform Invoke (P/Invoke) | Microsoft Docs[^].
 
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I suspect you're going to have to create a DLL that can talk to the C++ DLL, and which exports a plain C version of the API. Then, you can use that DLL from C#.

C++ <-> C <-> C#
 
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Importing an class isnt always the best idea, but importing the data is more simple. You cant import classes with members of classes which arent supported.

Read my article Calling-All-Stations and its code about a possible solution.
When transfering string between C++ and C# the best solutions are simple char-arrays or the more complex _bstr_t.
 
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