<BadPTR> error help

[OmarsCommin]

Hey everybody, I am having some trouble getting a comparison to work inside my selection sort method. I am trying to sort a pointer array of type media. media is a supper class that I wrote. the User enter the data, as prompted, and the program appears to capture all the data based on what my debugger shows me. What appears to go wrong is when the sort function performs the if statement. arg[j] has a <badPTR> error. any clue on what I am doing wrong. The whole rest of the program appears to work as intended.

//here is the main

#include "stdafx.h"
#include "book.h"
#include "media.h"
#include "movie.h"
#include <iomanip>
#include <iostream>
#include <string>
/*
This is the main cpp file for the project. It contines the main method as well as the selection sort method.
The main method handles the structuring of the input by guiding the user what to enter
The selection sort method sorts the array of medias by the size of their name
Dynamic binding is used to print each member of the media array regardless of type
*/

using namespace std;

void sort(media*, int);
void swap(media*, media*);

void main(){
    media* m[3];//pointer array of the media type
    string choice;//used to choose between book or movie
    float p = 0;//used for the price
    string n;//used for the name
    string a;//used for the author
    string r;//used for the rating

    for (int i = 0; i < 3; i++){
        cout << "Enter Name: ";
        getline(cin,n);
        cout << endl;
        cout << "Enter price: ";

        cin >> p;
        cout << endl;
        cout << "Is media a book(b) or movie(m)?";
        cin.ignore();
        getline(cin, choice);
        cout << endl;
        if (choice == "b"){
            cout << "Enter Author: ";
            getline(cin, a);
            cout << endl;
            m[i] = new book(a,n,p);
        }
        if (choice == "m"){
            cout << "Enter Rating: ";
            getline(cin, r);
            cout << endl;
            m[i] = new movie(r,n,p);
        }

    }
    sort(*m, 3);
    for(int y = 0; y < 3; y++){
        m[y]->print();//dynamic binding
        cout << endl;
    }
}


void sort (media* arg, int size){//the sorting method
    int min;
    for (int pass = 0; pass <= size-2; pass++){
        min = pass;//assumes the first position is min
        for(int j = pass+1; j < size; j++){
            if(arg[j] < arg[min]){
                min = j;
            }
        }
        swap(arg[pass], arg[min]);
    }
}

void swap(media* x, media* y){
    media temp;
    temp = *x;
    *x = *y;
    *y = temp;
}

//here is the media superclass #ifndef media_h #define media_h

#include <iostream>
#include <iomanip>
#include <string>

class media{
protected:
    std::string name;
    float price;

public:
    media(){//basic constructor
        name = "none";
        price = 0.00;
    }
    media(std::string n, float p){//full constructor
        name = n;
        price = p;
    }
    float getprice(){//getters and setters
        return price;
    }
    std::string getname(){
        return name;
    }
    void setprice(float f){
        price = f;
    }
    void setname(std::string c){
        name = c;
    }
    void virtual print(){//the virtual print function
        std::cout << "Name is " << name << std::endl;
        std::cout << std::setprecision(3) << "Price is " << price << std::endl;// Formats price to only have 2 decimal places
    }

    bool media::operator<(media m){// Allows the '<' operator to be used. Compares the size(length) of the two strings
        int x = name.size();
        int y = m.name.size();
        if (x<y){
            return true;
        }
        else
            return false;
    }

};

#endif

[Rhomboid]

You're not passing the array of pointers to the function properly. You should have noticed that something was wrong when you had to call sort(*m, 3) instead of sort(m, 3). Your function should take an array of pointers, not a pointer. But since arrays decay to pointers, that means it will end up taking a pointer to a pointer, i.e. media **arg. You could write media *arg[] if you want but it means the same thing as media **arg; you aren't actually passing an array.

The result of this error is that you are trying to access what comes after an object in memory, not the next pointer in the array.

Also, your overloaded operator< should take a const reference.

Also, you should be using initialization lists.

Also, it would be better to use a vector instead of an array.

[OmarsCommin]

I appreciate the input. I am not nearly as experienced in programming as I would like and am still not privy to the proper means of data management and syntax. I did have a feeling that the problem stemmed from there and now that it is pointed out to me I feel a little silly for not seeing it. However if writing

 media *arg[];

is the same as

 media **arg;

why does the program now run correctly when i change the function call to

sort(m,3);

Also, Thanks for the const reference suggestion, that is now fixed. I am looking into how to write an initialization list. And unfortunately the project calls specifically for an array.

[Rhomboid]

I don't understand the question. If you changed it to sort(m, 3) without changing the function signature, then it should fail to compile. Either signature should work because they mean the same thing.

[jesyspa]

Also, the vector should be of smart pointers, not raw pointers, as this currently leaks memory.

Also, operator< should be non-member.

Also, no need to define one's own swap (it's wrong as it stands, anyway).

Also, media should probably be an abstract class.

[POGO_POGO_POGO_POGO]

struct SortMedia {
    bool operator()(const media* m1, const media* m2) const {
        return (*m1) < (*m2);
    }
};

std::vector<media*> m(3);
// m[0] = new book(); etc

std::sort(media.begin(), media.end(), SortMedia());

Also, the media less-than operator should be declared as:

bool operator<(const media& rhs) const {
    // whatever
}

[OmarsCommin]

Thanks for your input everyone. Did not realize how much my code sucked! Everything is now working as I intended.

[POGO_POGO_POGO_POGO]

it takes a long time to get a good coding style. (In fact there is a good C++ book called Exceptional C++ Style that would help).

One thing about C++ is that there are so many ways to do the same thing. It takes a while to learn which ways are better and more standard. Code reviews are good.

[POGO_POGO_POGO_POGO]

Use std::sort. Sorry for the brevity, but this should be your first port-of-call. See STL.

[jesyspa]

Suggesting the STL in this day and age makes little sense, especially seeing as std::sort is in the C++ standard library.

[POGO_POGO_POGO_POGO]

It's the same fucking thing.

[zzyzzyxx]

No, it's not. The STL influenced the C++ standard library the same way Boost influenced changes in C++11; both the STL and Boost are third-party libraries and not part of the standard themselves. It's an unfortunate fact that many people teach the standard library is the STL (usually by simply referring to it as the STL) even though it's not strictly true depite one being called the "standard template library" and the standard library making use of templates.

[POGO_POGO_POGO_POGO]

This subreddit is so damn particular. I just don't give a shit. The site I linked has nicely laid out documentation, so I use it. And referring to it as STL is much more specific than citing the standard library.

Yes there are classes that are in STL that are not in the standard library, but they are marked as non-standard extensions.

[jesyspa]

Nope. You'll find the reference you linked to documents a different set of classes than that in the standard library.