#include int main() {
using std::cout;
using std::cerr;
// load the triangle library
void* triangle = dlopen(“./triangle.so”, RTLD_LAZY);
if (!triangle) {
cerr << "Cannot load library: " << dlerror() << '\n';
return 1;
}
// reset errors
dlerror();
// load the symbols
create_t* create_triangle = (create_t*) dlsym(triangle, “create”);
const char* dlsym_error = dlerror();
if (dlsym_error) {
cerr << "Cannot load symbol create: " << dlsym_error << '\n';
return 1;
}
destroy_t* destroy_triangle = (destroy_t*) dlsym(triangle, “destroy”);
dlsym_error = dlerror();
if (dlsym_error) {
cerr << "Cannot load symbol destroy: " << dlsym_error << '\n';
return 1;
}
// create an instance of the class
polygon* poly = create_triangle();
// use the class
poly->set_side_length(7);
cout << "The area is: " << poly->area() << '\n';
// destroy the class
destroy_triangle(poly);
// unload the triangle library
dlclose(triangle);
}
//———-
//polygon.hpp:
//———-
#ifndef POLYGON_HPP
#define POLYGON_HPP
class polygon {
protected:
double side_length_;
public:
polygon()
: side_length_(0) {}
virtual ~polygon() {}
void set_side_length(double side_length) {
side_length_ = side_length;
}
virtual double area() const = 0;
};
// the types of the class factories
typedef polygon* create_t();
typedef void destroy_t(polygon*);
#endif
//———-
//triangle.cpp:
//———-
#include “polygon.hpp”
#include class triangle : public polygon {
public:
virtual double area() const {
return side_length_ * side_length_ * sqrt(3) / 2;
}
};
// the class factories
extern “C” polygon* create() {
return new triangle;
}
extern “C” void destroy(polygon* p) {
delete p;
}
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