emplace back

[adam2016]

Hi guys I am writing a kind of self messaging maybe you could even call it a memo or notes to self console application,very simple stuff

I am trying to use the emplace_back function on std::vector I read that it came into existence in c++11 so I enabled c++11 in my build settings but I am still getting an error


the reason I want to do this is because I want to create a vector of ofstreams and since the copy constructor cannot be called for ofstreams I need to use the emplace back function

here is the error I am getting pretty much saying it is a deleted function,also it will show the error on line 75 of stl_constructs header file



\CodeBlocks\MinGW\lib\gcc\mingw32\4.9.2\include\c++\bits\stl_construct.h|75|error: use of deleted function 'std::basic_ofstream<char>::basic_ofstream(const std::basic_ofstream<char>&)'|


thanks

#include <iostream>
#include <algorithm>
#include <vector>
#include <fstream>
#include <limits>

using namespace std;

class message
{

public:
    string title;
    string time;

    message(string t,string tm)
        : title(t),time(tm)
    {
    }

    string getHeader(const string& header)
    {

        if(header == "title")
        {

            return title;
        }
        if(header == "time")
        {

            return time;
        }
    }
};

class messageSorter
{


public:
    string field;

    messageSorter(string f)
        :field(f)
    {}

    bool operator()(message& lhs,message& rhs)
    {

        return lhs.getHeader(field) < rhs.getHeader(field);
    }
};

class account
{

public:

    string username;
    string password;
    vector<message> messages;

    account()
    {

        username = "";
        password = "";
    }

    account(string u,string p)
    {

        username = u;
        password = p;

    }
};

bool usernameNotTaken(vector<account> &accounts,string username)
{

    for(int i = 0; i < accounts.size(); i++)
    {

        if(username == accounts.at(i).username)
        {

            return false;
        }
    }
    return true;
}

bool createAccount(vector<account> &accounts,string &username,string &password,ofstream &accountsFileO)
{

    if(usernameNotTaken(accounts,username))
    {
        accounts.push_back(account(username,password));
        accountsFileO << username << endl;
        accountsFileO << password << endl;
        ofstream messagesFile;
        string fileName = username.append(".txt");
        messagesFile.open(fileName.c_str());
        cout << "success" << endl;
        return true;
    }
    cout << "sorry username taken will need a different name" << endl;
    return false;
}

bool enterNumber(int &num){

     if(cin >> num){

        return true;
     }else{
       cin.clear();
       cin.ignore(numeric_limits<streamsize>::max(), '\n');
       return false;
     }
}

void driver()
{
    vector<account> accounts;
    ofstream accountsFileO;
    ifstream accountsFileI;
    vector<ofstream> accountMessages;
    string username;
    string password;
    string createUser;
    string createPass;
    bool loggedIn = false;
    int newAccount;

    accountsFileO.open("accounts.txt",ios::app);

    if(!accountsFileO.is_open()){

        return;
    }

    accountsFileI.open("accounts.txt");

    if(!accountsFileI.is_open()){

        return;
    }
    // read in all accounts from file
    // and set up ofstreams for account messages

    while(accountsFileI){

        string name;
        string pass;

        accountsFileI >> name;
        accountsFileI >> pass;

        string messagesFileName = name.append(".txt");
        ofstream tempOf;
        tempOf.open(messagesFileName.c_str());
        accountMessages.emplace_back();

        account temp(name,pass);
        accounts.push_back(temp);
    }


    cout << "***** WELCOME TO THE MESSAGES SERVICE ****** " << endl;
    cout << "are you not a member want to create an account? press 1 for yes " << endl;

    while(!enterNumber(newAccount)){

        cout << "wrong input,you entered characters? please re enter choice" << endl;
        cout << "are you not a member want to create an account? press 1 for yes " << endl;
    }

    if(newAccount == 1)
    {
        do
        {
            cout << "enter a username" << endl;
            cin >> createUser;
            cout << "enter a password" << endl;
            cin >> createPass;

        }
        while(!createAccount(accounts,createUser,createPass,accountsFileO));
    }
    cin.get();

    while(!loggedIn)
    {
        cout << "> enter username" << endl;
        getline(cin,username);
        cout << "> enter password" << endl;
        getline(cin,password);

        for(int i = 0; i < accounts.size(); i++)
        {

            if(username == accounts.at(i).username && password == accounts.at(i).password)
            {
                loggedIn = true;
            }
        }
    }
    if(loggedIn)
    {
        account thisAccount ;

        for(int i = 0; i < accounts.size(); i++)
        {
            if(username == accounts.at(i).username && password == accounts.at(i).password)
            {
                thisAccount = accounts.at(i);
            }
        }
        while(true)
        {
            int choice;
            cout << "view messages" << endl;
            cout << "press 1 to view by title,press 2 to view by time"
            << "3 to send message to self " << "press  to quit " << endl;
            while(!enterNumber(choice))
            {

                cout << "wrong input,you entered characters? please re enter choice" << endl;
                cout << "press 1 to view by title,press 2 to view by time"
                << "3 to send message to self " << "press  to quit " << endl;
            }
            cin.get();

            if(choice == 1)
            {
                sort(thisAccount.messages.begin(),thisAccount.messages.end(),
                     messageSorter("title"));
                for(int i = 0; i < thisAccount.messages.size(); i++)
                {

                    cout << thisAccount.messages.at(i).title <<
                         thisAccount.messages.at(i).time << endl;
                }
            }
            if(choice == 2)
            {

                sort(thisAccount.messages.begin(),thisAccount.messages.end(),
                     messageSorter("time"));
                for(int i = 0; i < thisAccount.messages.size(); i++)
                {

                    cout << thisAccount.messages.at(i).title <<
                         thisAccount.messages.at(i).time << endl;
                }
            }
            if(choice == 3)
            {

                string title;
                string time;

                cout << "enter title of message " << endl;
                getline(cin,title);
                cout << "enter time of message " << endl;
                getline(cin,time);

                thisAccount.messages.push_back(message(title,time));
            }
            if(choice == 4)
            {
                return;
            }
        }
    }
}

int main()
{
    driver();
}

[Peter87]

This code compiles fine for me with GCC 7.3 so my guess is that your compiler is simply too old.

[adam2016]

thanks Peter that is probably the reason

apart from updating my compiler is there any other way I can get around the copy constructor problem,

I could make my own vector class but that would take some time

[Peter87]

You could store pointers in the vector.

vector<ofstream*> accountMessages;
accountMessages.push_back(new ofstream);

If your compiler supports it you could use std::unique_ptr instead of raw pointer. That way you don't need to worry about memory leaks if you forget to use delete to destroy the ofstream objects when you are done using them.

[adam2016]

Hi Peter yes thats the idea I choose to use,

but then I ran into a problem with dereferencing the pointers

while(accountsFileI){

        string name;
        string pass;

        accountsFileI >> name;
        accountsFileI >> pass;

        string messagesFileName = name.append(".txt");
        ofstream* tempOf = new ofstream;
        tempOf->open(messagesFileName.c_str());
        accountMessages.push_back(tempOf);

        account temp(name,pass);
        accounts.push_back(temp);
    }

    for(int i = 0; i < accountMessages.size(); i++){

        string title;
        string time;

        while(!accountMessages.at(i)->eof()){

            *(accountMessages.at(i)) >> title; // will give me an error but not sure why
           // since I am just derefencing a pointer?
           // accountMessages.at(i) >> time;
        }

    }

[Peter87]

Stream operators should point in the direction of the data flow. In this case the data goes from title to the ofstream so the operator should point towards the ofstream.

*accountMessages.at(i) << title;

[adam2016]

oh my bad big mistake,I should have created an ifstream :o

totally slipped my mind,

thanks Peter