How could I implement a vector of stack? - c++

Question

I am currently trying to implement a class with a vector of stacks. The class shall work as a stack to other objects but distribute the data to different stacks of a maximum size internally. If a stack is full a new one is created and pushed to the internal vector.
My current approach generates errors:
prog.cpp: In instantiation of ‘SetOfStack<T>::SetOfStack(int) [with T = int]’:
prog.cpp:54:32: required from here
prog.cpp:13:17: error: no matching function for call to ‘std::vector<std::stack<int, std::deque<int, std::allocator<int> > >, std::allocator<std::stack<int, std::deque<int, std::allocator<int> > > > >::push_back(std::stack<int, std::deque<int, std::allocator<int> > >*)’
stacks.push_back( new stack<T> );
^
/usr/include/c++/4.8/bits/stl_vector.h:901:7: note: no known conversion for argument 1 from ‘std::stack<int, std::deque<int, std::allocator<int> > >*’ to ‘const value_type& {aka const std::stack<int, std::deque<int, std::allocator<int> > >&}’
/usr/include/c++/4.8/bits/stl_vector.h:919:7: note: void std::vector<_Tp, _Alloc>::push_back(std::vector<_Tp, _Alloc>::value_type&&) [with _Tp = std::stack<int, std::deque<int, std::allocator<int> > >; _Alloc = std::allocator<std::stack<int, std::deque<int, std::allocator<int> > > >; std::vector<_Tp, _Alloc>::value_type = std::stack<int, std::deque<int, std::allocator<int> > >]
push_back(value_type&& __x)
^
/usr/include/c++/4.8/bits/stl_vector.h:919:7: note: no known conversion for argument 1 from ‘std::stack<int, std::deque<int, std::allocator<int> > >*’ to ‘std::vector<std::stack<int, std::deque<int, std::allocator<int> > >, std::allocator<std::stack<int, std::deque<int, std::allocator<int> > > > >::value_type&& {aka std::stack<int, std::deque<int, std::allocator<int> > >&&}’
prog.cpp: In instantiation of ‘void SetOfStack<T>::push(T) [with T = int]’:
prog.cpp:55:21: required from here
prog.cpp:22:25: error: ‘__gnu_cxx::__alloc_traits<std::allocator<std::stack<int, std::deque<int, std::allocator<int> > > > >::value_type’ has no member named ‘push_back’
stacks[current_stack].push_back(new stack<T>);
^
prog.cpp: In instantiation of ‘T SetOfStack<T>::pop() [with T = int]’:
prog.cpp:56:27: required from here
prog.cpp:34:25: error: ‘__gnu_cxx::__alloc_traits<std::allocator<std::stack<int, std::deque<int, std::allocator<int> > > > >::value_type’ has no member named ‘pop_back’
stacks[current_stack].pop_back();
^
Sample Code:
#include <iostream>
#include <stack>
#include <vector>
using namespace std;
template <class T>
class SetOfStack {
public:
SetOfStack( int max_size ): current_stack(0), max_stack_size(max_size) {
stacks.reserve(10);
stacks.push_back( new stack<T> );
}
~SetOfStack() {
stacks.clear();
}
void push( T value ) {
stacks[current_stack].push(value);
if(stacks[current_stack].size() > max_stack_size) {
stacks[current_stack].push_back(new stack<T>);
current_stack++;
if(current_stack % 10 == 0 && current_stack > stacks.size()) {
stacks.reserve(stacks.size() + 10);
}
}
}
T pop() {
T value = stacks[current_stack].top();
stacks[current_stack].pop();
if(stacks[current_stack].size() == 0 && current_stack != 0 ) {
stacks[current_stack].pop_back();
current_stack--;
}
}
T popAt( int index ) {
T value = stacks[index].top();
stacks[index].pop();
}
private:
int current_stack;
int max_stack_size;
vector< stack<T> > stacks;
};
int main() {
// Test code
SetOfStack<int> s_o_s(3);
s_o_s.push(1);
cout << s_o_s.pop() << endl;
return 0;
}

Answer 1

The error you're getting is this line:
stacks.push_back( new stack<T> );
As well as this line:
stacks[current_stack].push_back(new stack<T>);
Because you have declared stacks as a non-pointer:
vector< stack<T> > stacks;
So you want to use just stack<T>() instead of new stack<T>
Additionally, std::stack does not have a function push_back, you need to use push instead.
stacks.push_back(stack<T>());
stacks[current_stack].push(value);
As well as pop and not pop_back():
stacks[current_stack].pop();
At which point, you no longer need the deletes I mentioned in my original comment, since it looks like you were not intending to call new