I have the following main program that creates a Stack object, fills it with doubles and then pops them. The code files fine, but the pop_back() part does not seem to work, while s.back() does return the correct value. How is this possible?
#include "Stack.h"
#include <iostream>
#include <deque>
using namespace std;
int main() {
Stack<double> s(0,0.0);
// Write doubles into Stack
int i ;
for (i=0 ; i<15 ; i++) {
s.push(i*i) ;
}
// Read doubles back from fifo
while (!s.empty()) {
double val = s.pop() ;
std::cout << "Popping value " << val << " from stack" << std::endl ;
}
return 0 ;
}
My header file looks like this, where I have omitted parts which are not relevant to the question.
#ifndef STACK_H
#define STACK_H
#include <iostream>
#include <deque>
template<class T>
class Stack {
public:
Stack(int len, T defval): s(len+1, defval) {
return;
}
~Stack() {
//delete [] s;
}
void push(T c) {
s.push_back(c);
}
T pop() {
return s.back();
s.pop_back();
}
private:
std::deque<T> s; //Array<T> s;
};
#endif
T pop() {
return s.back();
// ^^^^^
s.pop_back(); // <- unreachable!
}
When you return from a function, all the subsequent instruction will never be executed.
Store s.back()'s result in a temporary variable instead:
T pop() {
auto back = s.back();
s.pop_back();
return back;
}