How Can I Create and Use Dynamic Shared C Class Libraries on Linux?

Dynamic Shared C Class Libraries on Linux

Introduction
Creating and utilizing shared class libraries in C on Linux can be a challenging task. This article provides a comprehensive guide that covers the process of creating and using shared C class libraries, including object creation, modification, and destruction.

Creating a Shared C Class Library
To create a shared C class library, follow these steps:

1. Define the class interface: Create a header file (.h) that declares the class interface, including member variables and methods.
2. Implement the class methods: Create a source file (.cc) that implements the class methods.
3. Export the library functions: Use "extern 'C'" to export the functions that will be used to create and destroy library objects.
4. Compile the library: Compile the header and source files into a shared library using the appropriate flags (-shared on Linux, -dynamiclib on macOS).

Using a Shared C Class Library
To use a shared C class library that has been created, follow these steps:

1. Load the library: Use dlopen() to load the shared library into memory.
2. Resolve function symbols: Use dlsym() to resolve the addresses of the exported functions.
3. Create and use library objects: Use the function pointer retrieved from dlsym() to create objects of the library class and call their methods.
4. Destroy library objects: When finished, use the destruction function pointer to properly destroy the library objects.

Example Implementation
The following code snippets demonstrate a simple shared C library (myclass.h, myclass.cc) and a C program (class_user.cc) that utilizes the library:

myclass.h:

class MyClass {
public:
  MyClass();
  virtual void DoSomething();
private:
  int x;
};

myclass.cc:

extern "C" MyClass* create_object() { return new MyClass; }
extern "C" void destroy_object(MyClass* object) { delete object; }
MyClass::MyClass() { x = 20; }
void MyClass::DoSomething() { cout << x << endl; }

class_user.cc:

MyClass* (*create)();
void (*destroy)(MyClass*);
create = (MyClass* (*)())dlsym(handle, "create_object");
destroy = (void (*)(MyClass*))dlsym(handle, "destroy_object");
MyClass* myClass = (MyClass*)create();
myClass->DoSomething();
destroy(myClass);

Compilation (Linux):

g++ -fPIC -shared myclass.cc -o myclass.so
g++ class_user.cc -ldl -o class_user

By following these steps, you can successfully create and use dynamic shared C class libraries on Linux.

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