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Editorial Team
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Asked: 2026-05-20T18:57:10+00:00

I am new to .net . I have a managed C++ library. It looks

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I am new to .net .
I have a managed C++ library. It looks like this.

// header file
namespace cppnetdll
{
public __gc class Class1
{
public:
static int foo_int(void);
};
}

// source file
namespace cppnetdll
{
int Class1::foo_int(void)
{
return 123;
}
}

I can call this from a managed c++ program. When I try to call it from
a C# program, I get the compiler error: “The type or namespace name
‘Class1’ could not be found (are you missing a using directive or an
assembly reference?)” The error refers to the DllImport line below.

Here is the C# code
[code:1:a72c1df571]
namespace csuser
{
public class xxx
{
[DllImport(“cppnetdll.dll”)] extern
int Class1.foo_int();

private void yyy() { int i =
foo_int(); }
}
}[/code:1:a72c1df571]

I have tried various approaches but no success. What is the magic
syntax ?

It’s funny that I can call unmanaged C++ functions from C# fairly
easily by declaring the functions as “C” and exporting from the DLL.
I expected calling managed code to be easier. Maybe it’s so easy
that no one thought of documenting it !

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1 Answer

  1. Editorial Team

    You do not use a [DllImport] directive to call code that’s written in managed C++. That is only intended for native DLLs that export their functions. Neither of which applies to yours, it isn’t native and you don’t export the function.

    You built a managed assembly, you can treat it just like one you’d have written in C#. Project + Add Reference, Browse tab, navigate to the DLL. Or better yet, put both projects in one solution, use the Projects tab to select the reference.

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