Thread: keeping the class alive

hi,

How can I keep my class and all datastructures alive in the following example:

Code:

class A{

  protected:
   
    vector<int> x;
 
  public:

  A();
 
  ~A();
};

A::A(){
  x.resize(10);
  for (int i =1; i< 10; i++)
    x[i] = i;
}
A::z(){
  cout << x[1] << endl;
}

class B : protected A {

  public:

  B();

  int f();

};

B::B(){

  A obj;
}

B::f(){
  this->z();
}

int main(){
  B o();
  
  o.f();  // it should print 1 but vector is of size 0 since, I guess it want out of scope;

}

so the idea is to construct class B from main which constructs class A. And after the construction I whish to call function f which calles function z of A but z cannot execute since vector x is empty. Why is it empty and how to keap it full untill B is destroyed?

thnx

PS
I tried to illustrate the concept thus code might not be functionall

I must be doing something seriously wrong. I was in a hurry before but now here is the actuall example

Code:

#include <iostream>
#include <vector>
#include <string>

using namespace std;


template<typename T>
class AA{
protected:

   vector<T> vx;
public:

  AA(vector<T>& v);

};

template<typename T>
AA<T>::AA(vector<T>& vec){
  vx.reserve(vec.size());
  copy(vec.begin(),vec.end(),back_inserter(vx));
}


// my derived class
template<typename T>
class B : public AA {

  public:

  B(vector<T>& v);

  void print_r(T x);
};

template<typename T>
B<T>::B(vector<T>& vec){

  AA<T> a(vec);
}

template<typename T>
void B<T>::print_r(T x){
  cout << this->vx[x] << endl;
}

int main (){
  vector<int> V(10,6);
  int k = 4;
  B<int> b(V);
  b.print_r(k);
}

my error states:

Code:

$ g++ -g  -std=c++0x -o class_1 class_1.cpp
class_1.cpp:28:21: error: expected class-name before ‘{’ token
class_1.cpp: In member function ‘void B<T>::print_r(T) [with T = int]’:
class_1.cpp:51:14:   instantiated from here
class_1.cpp:44:3: error: ‘class B<int>’ has no member named ‘vx’

How to make this work ?

ok lets correct this:

Code:

#include <iostream>
#include <vector>
#include <string>
 
using namespace std;
 
 
template<typename T>
class AA{
protected:
 
   vector<T> vx;
public:
 
  AA(vector<T>& v);
 
};
 
template<typename T>
AA<T>::AA(vector<T>& vec){
  vx.reserve(vec.size());
  copy(vec.begin(),vec.end(),back_inserter(vx));
}
 
 
// my derived class
template<typename T>
class B : public AA<T> {  // corrected
 
  public:
 
  B(vector<T>& v);
 
  void print_r(T x);
};
 
template<typename T>
B<T>::B(vector<T>& vec){
 
  AA<T> a(vec);
}
 
template<typename T>
void B<T>::print_r(T x){
  cout << this->vx[x] << endl;
}
 
int main (){
  vector<int> V(10,6);
  int k = 4;
  B<int> b(V);
  b.print_r(k);
}

now i get an error :

Code:

t$ g++ -g  -std=c++0x -o class_1 class_1.cpp
class_1.cpp: In constructor ‘B<T>::B(std::vector<T>&) [with T = int]’:
class_1.cpp:51:13:   instantiated from here
class_1.cpp:38:23: error: no matching function for call to ‘AA<int>::AA()’
class_1.cpp:38:23: note: candidates are:
class_1.cpp:20:1: note: AA<T>::AA(std::vector<T>&) [with T = int]
class_1.cpp:20:1: note:   candidate expects 1 argument, 0 provided
class_1.cpp:9:7: note: AA<int>::AA(const AA<int>&)
class_1.cpp:9:7: note:   candidate expects 1 argument, 0 provided
class_1.cpp:9:7: note: AA<int>::AA(AA<int>&&)
class_1.cpp:9:7: note:   candidate expects 1 argument, 0 provided

that is it , thank you laserlight now I have all the pieces for my study case. I'll bug you more if i don't connect the dots thank you once again !