How do I share a constant between C# and C++ code?

Question

I\'m writing two processes using C# and WCF for one and C++ and WWSAPI for the second. I want to be able to define the address being used for communication between the two

Answer 1

You can create a separate C++/CLI project and define all your constants in a .h file. For example, create C++/CLI Class Library project called "ConstantBridge" and a C# project called "CSharpProgram":

Constants.h

namespace Constants
{
    const int MAGIC_NUMBER = 42;
}

// String literals must be defined as macros
#define MAGIC_PHRASE "Hello World"

// Since stirngs must be macros it's arguably more consistent 
// to use `define` throughout. This is for demonstration purpose.

ConstantBridge.h

#include "Constants.h"

namespace ConstantBridge { public ref class ConstantBridge {
public:
    // The use of the `literal` keyword is important
    // `static const` will not work
    literal int kMagicNumber = Constants::MAGIC_NUMBER;
    literal String ^ kMagicPhrase = MAGIC_PHRASE;
};}

CSharpProgram.cs

Console.WriteLine(ConstantBridge.kMagicNumber); // "42"
Console.WriteLine(ConstantBridge.kMagicPhrase); // "Hello World"

Now, have the "CSharpProgram" project reference the "ConstantBridge" project. Your other native C++ projects can simply #include "Constants.h".

As long as you reference only literals from the ConstantBridge project, a runtime dependency will not be generated. You can verify using ILSpy or ILdasm. const in C# and literal in C++/CLI are copied "literally" to the call site during compilation.