c++ - Access child struct values in vector -

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• what object slicing? 15 answers

i have object structs this:

struct object {    string type;    color c;    float ambient, diffuse; };  struct sphere: object {    point center;    float radius; };  struct square: object {    point loc;    float len; }; 

and have vector filled sphere , square structs:

vector<object> objs; sphere sp = //sphere stuff square sq = //square stuff objs.push_back(sp); objs.push_back(sq); 

i can access values in parent struct fine, having trouble figuring out how access values in sphere , square structs. doing right now:

cout << objs.at(i).type << endl; //this works cout << objs.at(i).center.x << endl; //not working 

does know how this?

you can't, don't exist more. not storing squares or spheres in vector, storing objects. should read what object slicing?.

that said, if instead store pointers objects, std::vector<object*> pass pointers objects of derived types. how know element in vector square , sphere. whole purpose of having base class provide interface functionality want, through virtual function, derived classes implement in different ways:

struct base {     virtual void foo() { std::cout << "foo in base\n"; } }; struct derived1 : base {     void foo() override { std::cout << "foo in derived1\n"; } }; struct derived2 : base {     void foo() override { std::cout << "foo in derived2\n"; } };  derived2 d; base* b = &d; b->foo(); // prints "foo in derived2\n" 

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that said, square* object*, use static_cast<square*>(objp) if know sure square, , dynamic_cast<square*>(objp) if not (it return null pointer if wrong). having indicates bad design though!

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also, please reconsider use of considered bad practices: using namespace std; , endl (those links explanations).