How Can I Create and Use Dynamic Shared Libraries (DSLs) in C on Linux?

Creating and Using Dynamic Shared Libraries in C on Linux

Dynamic shared libraries (DSLs) allow multiple programs to share code, reducing memory usage and improving efficiency. In C , DSLs enable the creation of reusable class libraries accessible to multiple executables.

Creating the DSL

To create a DSL, define the class interface and implementation in header and source files (e.g., myclass.h and myclass.cc). Ensure the class includes a virtual destructor and public methods marked extern "C" to facilitate symbol loading.

Using the DSL

To utilize a DSL in a separate executable, perform the following steps:

1. Include necessary libraries () and headers.
2. Use dlopen() to load the shared library.
3. Access the library's functions and symbols using dlsym().
4. Call the create_object() function to instantiate an object from the library class.
5. Call the object's methods.
6. Destroy the object using destroy_object().

Example Code

myclass.h

#include <iostream>

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

myclass.cc

#include "myclass.h"

extern "C" MyClass* create_object() {
  return new MyClass;
}

extern "C" void destroy_object(MyClass* object) {
  delete object;
}

MyClass::MyClass() {
  x = 20;
}

void MyClass::DoSomething() {
  std::cout << x << std::endl;
}

class_user.cc

#include <dlfcn.h>
#include <iostream>
#include "myclass.h"

int main() {
  void* handle = dlopen("./myclass.so", RTLD_LAZY);
  MyClass* (*create)();
  void (*destroy)(MyClass*);

  create = (MyClass* (*)())dlsym(handle, "create_object");
  destroy = (void (*)(MyClass*))dlsym(handle, "destroy_object");

  MyClass* myClass = create();
  myClass->DoSomething();
  destroy(myClass);
}

Compilation and Execution

On Mac OS X:

• Compile the DSL: g -dynamiclib -flat_namespace myclass.cc -o myclass.so
• Compile the user executable: g class_user.cc -o class_user

On Linux:

• Compile the DSL: g -fPIC -shared myclass.cc -o myclass.so
• Compile the user executable: g class_user.cc -ldl -o class_user

Execute class_user to use the MyClass shared library. It will instantiate and utilize the MyClass object successfully.

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