Thread: const confusion

Code:

prototypes:
void edit_book(map<string,Book> *);
map<string,Book> *get_ptrLibrary() const {return ptrLibrary;};


call to function: error here
edit_book(get_ptrLibrary());

I am getting the following error:
editmenu.cpp:46: passing `const EditMenu' as `this' argument of `void
EditMenu::edit_book(std::map<std::string, Book, std::less<std::string>,

std::allocator<std::pair<const std::string, Book> > >*)' discards qualifiers

I think this has to do with my const declaration
I want edit_book(map<string,Book> *) to be able to change the map but get_ptrLibrary() shouldn't alter anything therefore is a const function. What exactly is the problem here?

Post the whole class & function where error happens code please.

The whole file:

Code:

#include <iostream>
using std::cout;
using std::endl;
using std::left;

#include <iomanip>
using std::setw;

#include <map>
using std::map;

#include "menu.h"
#include "book.h"
#include "editmenu.h"

EditMenu::EditMenu(){}

EditMenu::EditMenu(std::map<string,Book> & rlibrary){
    ptrLibrary=&rlibrary;
}

void EditMenu::display_menu() const{
    cout << "\t\tEdit Menu\n";
    cout << "1.  Display Library\n";
    cout << "2.  Edit Book\n";
    cout << "3.  Remove Book\n";
    cout << "4.  Add Book\n";
    cout << "5.  Display Book\n";
    cout << "6.  Main Menu"<<endl;
}

bool EditMenu::validate_option(int noption) const{
    bool valid;
    if (noption>=0 && noption<=6)
        valid=TRUE;
    else
        valid=FALSE;
    return valid;
}
void EditMenu::process_option(int noption) const{
    switch (noption){
            case 1: display_library(get_ptrLibrary());
                    break;
                    
            case 2: {
                        edit_book(get_ptrLibrary());  
                    }
                    break;
                    
            case 3:                         
            case 4:
            case 5:
            case 6:
            default:
                    break;
                
    }
}
void EditMenu::display_library(map<string,Book> *ptrLib) const{
    cout << setw(8)<<left<<"ISBN"
         << setw(24)<<left<<"  Title"<<endl;
    
    map<string,Book>::iterator pos;
    for (pos=ptrLib->begin();pos !=ptrLib->end();++pos){
        cout << "--------------------------------------------\n";
        cout << setw(10)<<left<<pos->second.get_ISBN()
             << setw(60)<<left<<pos->second.get_title()<<endl;
    }   
}

 

void EditMenu::remove_book(map<string,Book> *ptrLib){}
void EditMenu::add_book(map<string,Book> *ptrLib){}
void EditMenu::edit_book(map<string,Book> *ptrLib){
string ttitle;
    cout << "Enter Book Title: ";
    cin >> ttitle;
    cin.ignore();
    map<string,Book>::iterator pos;
    pos=ptrLib->find(ttitle);
    cout <<pos->second;
    cin >>pos->second;
    cout endl;
    
}

You are calling a non-const member function:

Code:

void EditMenu::edit_book(map<string,Book> *ptrLib)

From a const function:

Code:

void EditMenu::process_option(int noption) const

That is, in a const function, the this pointer is const too, so, passing it to a non-const function makes it lose its qualifiers.

Darn, I guess I am going to have to edit process_option to be non constant from my base class to my derived classes. Should have thought of this in the beginning.