eclipse - C++ Class Constructor Argument: How to access members and methods from another class instance without copying? -

i have 2 classes a , b. in a, have members , methods, e.g.,

header files:

a.hpp:

    class {          public:         a(int i);         virtual ~a();         int j;         eigen::vector3d e;         void printe();     } 

b.hpp:

class b {   public:       b(a* a_ptr);       virtual ~b();       void dosomething();   private:       * object; }; 

source files:

a.cpp:

#include <iostream> #include "a.hpp" using namespace eigen; using namespace std;  a::a(int i) {   j = i; } a::~a() { } a::printe() {   cout<<"e = ("<<this->e(0)<<","<<this->e(1)<<","<<this->e(2)<<")"<<endl; } 

b.cpp:

#include <iostream> #include "a.hpp" #include "b.hpp" using namespace eigen; using namespace std;  b::b(const * a_ptr) {   object = a_ptr; } b::~b() { } b::dosomething() {   int = 2*object->j+object->e(1); // stupid , simple example }   

}

in class b, access members methods of instance of a, without copying anything. thought passing pointer instance of a constructor of b , access desired members , methods.,

this code above abstraction of problem, hope point. code compiles fine (i use eclipse luna), except when try create instance of class b

#include "a.hpp" #include "b.hpp" using namespace eigen; using namespace std;  int main(int argc, char **argv) {   a_instance(n);    a* a_ptr;   a_ptr = &a_instance;   b b_instance(a_ptr); // commenting line, code compiles fine    return 0; } 

when compiling code, eclipse outputs these errors:

errors (3 items)     make: *** [all] error 2     make[1]: *** [some_path.dir/all] error 2     make[2]: *** [some_other_path] error 1 

which unfortunately not me lot.

my question is: best way this? maybe better use friend class or inheritance? (note a makes computations required b, otherwise not related.) or doing wrong when passing pointer argument in constructor of b?

void dosomethingb(a_ptr->a); 

this not valid member function declaration nor definition.

you may want write

void dosomethingb() {     a_ptr->a; // want it? }