How to fix 'std::bad_alloc'

Question

I have to read from file 100 task of a different kind in order to do different operation on a Queue, and print on an output file. But I get "terminate called after throwing an instance of 'std::bad_alloc' " As Error I think is something in template declaration. I tried to declare it in different ways but seems not to work. If someone can help me I'll be very gratefull.

#include    <iostream>
#include    <fstream>
#include    <string>

#define INPUT_FILE "input.txt"
#define OUTPUT_FILE "output.txt"
using namespace std;


template <typename T> class Pila
{
private:
bool empty=1;
public:
int lunghezza;
int cima;
T * Tab;
    Pila(int L){
        lunghezza=L;
        Tab= new T[L];
        cima=lunghezza;
    }
    void Push(T L){  
        cima--;
        Tab[cima]=L;
    }

    void Pop(){

        if(!empty)
        cima++;
        if(cima=lunghezza) empty=1;
    }

    bool Empty(){
       if(empty==1) return 1;
       else return 0;
    }

    T top(){
        return Tab[cima];
    }


    void Print(){
        for(int i=lunghezza-1; i>=cima; i--) cout<< Tab[i]<< " ";
    }
};

template <typename V> class Queue
{

public:
    int lunghezza;

    Queue(int l){
        lunghezza=l;
    };
    Pila<V> A= Pila <V>(lunghezza);
    Pila<V> B= Pila <V>(lunghezza);

    void enqueue(V L){ //sposta tutti gli elementi da A a B 
        while(!A.Empty()){ 
            B.Push(A.top());
            A.Pop();
        }

        A.Push(L); //Mette L dentro A

        while(!B.Empty()){   //sposta tutto di nuovo dentro A
            A.Push(B.top());
            B.Pop();
        }
    }


    void dequeue(){
        if(A.Empty()){
            cout<< " Coda Vuota"<< endl;
        }
        else       
        A.Pop();
    }    

    void Stampa(){
            A.Print();
            cout<< endl; 
    }
};

int main(){


    fstream infile, outfile;

    infile.open(INPUT_FILE, fstream::in);
    outfile.open(OUTPUT_FILE, fstream::out);


    int c=0, N,tmp;
    string tipo,operazione;
    while(c<100){
        infile>> tipo;
        infile>> N;
       if(tipo=="int"){
            Queue<int> A(N);
            for(int i=0; i<N; i++){
                infile>> operazione;
                if(operazione=="dequeue")
                A.dequeue();
                else
                {
                    int elem=stoi(operazione.substr(1));
                    A.enqueue(elem);
                }

            }
            A.Stampa();
        }

        if(tipo=="double"){
            Queue<double> A(N);
            for(int i=0; i<N; i++){
                infile>> operazione;
                if(operazione=="dequeue")
                A.dequeue();
                else
                {
                    double elem=stod(operazione.substr(1));
                    A.enqueue(elem);
                }

            }
            A.Stampa();
        }


        if(tipo=="bool"){
            Queue<bool> A(N);
            for(int i=0; i<N; i++){
                infile>> operazione;
                if(operazione=="dequeue")
                A.dequeue();
                else
                {
                    bool elem=stoi(operazione.substr(1));
                    A.enqueue(elem);
                }

            }
            A.Stampa();          
        }

        if(tipo=="char"){
            Queue<char> A(N);
            for(int i=0; i<N; i++){
                infile>> operazione;
                if(operazione=="dequeue")
                A.dequeue();
                else
                {
                    char elem=(char)(operazione[1]);
                    A.enqueue(elem);
                }

            }
           A.Stampa();           
        }


        c++;
    }

}

Answer 1

Your first problem is in your initialization.

int lunghezza;

Queue(int l){
    lunghezza=l;
};
Pila<V> A= Pila <V>(lunghezza);
Pila<V> B= Pila <V>(lunghezza);

A and B will be initialized with the value of lunghezza which is not yet initialized. This way you can get a very high value that allocate lots of memory.

A better implementation of this part is to use initializers

int lunghezza;

Queue(int l) : lunghezza(l), A(l), B(l)
{
}

Pila<V> A;
Pila<V> B;

You second problem is in Pila class.

Pila(int L){
    lunghezza=L;
    Tab= new T[L];
    cima=lunghezza;
}

In this code, Tab is never disallocated so you will leak (loose) the allocated memory when your object will be destroyed. You must call delete[] Tab; in your destructor.

You can also use STL classes such as std::list or std::vector to replace your class Pila.