CODEWITHSUNDEEP
c++visual-c++
mathew
mathew

Reputation: 3

Difficulty with map's find function

I am having trouble figuring out why this is not compiling. This is just the basic class declaration, constructor/destructor and other functions are left out. Message is also properly defined somewhere else.

#include <vector>
#include <map>
using namespace std;
class SmartCarrier {
        map<string, vector <Message *>> accounts_map;
        void SearchMessage() const;

    };

When I try to assign m_iter with m_iter = accounts_map.find(account) I get the error no operator "=" matches these operands. I double checked to make sure the map iterator was the same type as the actual map which it is. I'm not sure what is incorrect.

void SmartCarrier::SearchMessage() const {
        string account;
        map<string, vector<Message *>>::iterator m_iter;
        cout << "Enter an account: ";
        cin >> account;
        try {
            m_iter = accounts_map.find(account);
            if (m_iter != accounts_map.end) {
                  //code to display account information
            } else {
                throw 'e';
            }
        } catch (char e) {
            cout << "Error: Account not found\n";
        }
    }

Upvotes: 0

Views: 50

Answers (1)

Remy Lebeau
Remy Lebeau

Reputation: 598279

SearchMessage() is declared as const, so its this parameter is pointing at a const SmartCarrier object, so its accounts_map member is also const. When find() is called on a const map, it returns a const_iterator instead of an iterator.

Also, accounts_map.end needs to be accounts_map.end() instead.

Also, using an exception the way you are is just wasted overhead that you can (and should) get rid of.

Try this:

void SmartCarrier::SearchMessage() const {
    string account;
    cout << "Enter an account: ";
    cin >> account;
    map<string, vector<Message *>>::const_iterator m_iter = accounts_map.find(account);
    if (m_iter != accounts_map.end()) {
        //code to display account information
    } else {
        cout << "Error: Account not found\n";
    }
}

If you are using C++11 or later, consider using auto instead of const_iterator explicitly, that would also fix the error:

auto m_iter = accounts_map.find(account);

Upvotes: 2

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