How to create a C++ Header File for DLL (Dynamic Link Library)?

Using a Dynamic Link Library (DLL) is a great way to reuse code. Rather than re-implementing the same routines in every program that you create, you write them one time and then reference them from apps that require the functionality. By putting code in the DLL, you save space in every app that references it, and you can update the DLL without recompiling all of the apps that use it.

The first step to build a static library is to create a header (.h file) to represent the API of the library as shown in this tutorial:

1. Create the header file, MathLibrary.h, with a text editor:

// MathLibrary.h - Contains declaration of Function class  
#pragma once  

#ifdef MATHLIBRARY_EXPORTS  
#define MATHLIBRARY_API __declspec(dllexport)   
#else  
#define MATHLIBRARY_API __declspec(dllimport)   
#endif  

namespace MathLibrary  
{  
    // This class is exported from the MathLibrary.dll  
    class Functions  
    {  
    public:  
        // Returns a + b  
        static MATHLIBRARY_API double Add(double a, double b);  

        // Returns a * b  
        static MATHLIBRARY_API double Multiply(double a, double b);  

        // Returns a + (a * b)  
        static MATHLIBRARY_API double AddMultiply(double a, double b);  
    };  
}

2. Save the header file with your library source file. It is needed when you compile your library source code.

3. Send header file to anyone who wants to use your library. They need it to compile their application source code.

⇒ "MathLibrary.cpp" - Build DLL Library

⇐ "MyExecRefsLib.cpp" - Reference Static Library

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