Question

I am trying to do some practice for memory allocation.

I have the below code which is working but have two questions.

Where do I have to use delete [ ] to free the memory after allocating?

Why is the output for this code at function when using show() function is CDcar?.

#include <cstdlib>
#include <new>
#include <iostream>
#include <cstring>
using namespace std;

class automobile {

    private:

        char (*function)[30];
        char *type;
        double speed;

    public:

        automobile ( );
        automobile (double , char *);
        void speed_up (double);
        void speed_down(double);
        const char * get_function ( ) const;
        void show ( );

};

automobile::automobile ( ) {

    speed = 0;
    function = new char [1][30];
    strcpy(function[1], "CD player with MP3");

    type = new char [4];
    strcpy(type, "car");

}

automobile::automobile(double spd, char * fn ) {

    int sz;

}

void automobile::show ( ) {

    cout << "This is a " << type << " and it has the following functions: " << function[1] << ", and its speed is " << speed << " km/h\n"; 

}

int main ( ) {

    automobile car;

    car.show ( );

    return 0;
}

this is the output:

This is a car and it has the following functions: CDcar, and its speed is 0 km/h

I thought the output shoud be this:

This is a car and it has the following functions: CD player with MP3, and its speed is 0 km/h

Please advise

Answer 1

Where do I have to use delete [ ] to free the memory after allocating?

Ideally nowhere. new and delete are features of C++ that are not suitable for most code. They are error-prone and too low-level. They’re only useful for basic building blocks.

The code shown could benefit from basic building blocks like std::string, std::vector.

---

The code shown also invokes undefined behaviour at least in one place:

function = new char [1][30];
strcpy(function[1], "CD player with MP3");

Arrays are 0-based, so function[1] is an out-of-bounds access.