Setter not changing the data from a vector within a class - c++

In my program, I have a class that holds a vector of type integer. It is used to store distances. I have a function, that when called, should set values in the vector to 0's. (used for initializing). But when I go to check the size of the vector, it still says the vector is empty.
I have created multiple functions that check whether the vector is adding any elements, and it is not. I have a function, that within main, I call to see if the vector is empty, and it returns 0 (the vector has 0 elements in it).
int MLB::getDistanceSize()
{
return distances.size();
}
void MLB::setInitialDistances(int size)
{
for(int i = 0; i < size; i++)
{
this->distances.push_back(0);
}
}
class MLB
{
public:
//constructor
MLB();
~MLB();
int getDistanceSize();
void setInitialDistances(int size);
private:
vector<int> distances;
};
The input file is a csv file with each line consisting of:
stadium1,stadium2,distance
so sample input file is:
AT&T Park,Safeco Field,680
AT&T Park,Oakland–Alameda County Coliseum,50
Angel Stadium,Petco Park,110
Angel Stadium,Dodger Stadium,50
Busch Stadium,Minute Maid Park,680
Busch Stadium,Great American Ball Park,310
Busch Stadium,Target Field,465
Busch Stadium,Kauffman Stadium,235
etc...
I am using qt, and this is where I am calling the functions themselves. All information is stored into a map, and the other getters work perfectly fine. Sorry for making this a lot more confusing than the problem really is, any help is greatly appreciated.
// key and value, key is the team name, value is the MLB stadium information
struct entry
{
string key;
MLB value;
};
class Map
{
public:
//Public default constructor
Map();
//Public default destructor
~Map();
// returns entry of the map
entry atIndex(int index);
// Inserts a key and its value using linear algorithm
void insert(const string& theKey, const MLB& value);
private:
vector<entry> thisTable;
int currentSize; //Integer variable for current size
};
functions for Map:
Map::Map()
{
currentSize = 0;
}
Map::~Map()
{
}
void Map::insert(const string& theKey, const MLB& value)
{
entry thisEntry;
thisEntry.key = theKey;
thisEntry.value = value;
thisTable.push_back(thisEntry);
currentSize+=1;
}
entry Map::atIndex(int index)
{
return thisTable.at(index);
}
//mainwindow constructor
mainWindow::mainWindow()
{
//Reads in input from first csv file, all works fine all data stored and can access it
string iStadium1;
string iStadium2;
string iDistance;
string previous;
int distance;
int index1;
int index2;
bool found;
ifstream csvFile2;
csvFile2.open("inputDistance.csv");
getline(csvFile2, iStadium1, ',');
while(!csvFile2.eof())
{
index1 = 0;
found = false;
while(!found)
{
if(thisMap.atIndex(index1).value.getStadiumName() == iStadium1)
{
thisMap.atIndex(index1).value.setInitialDistances(thisMap.mapSize());
cout << "Distance Size Test 1: " << thisMap.atIndex(index1).value.getDistanceSize() << endl;
found = true;
}
else
{
index1++;
}
}
previous = iStadium1;
while(iStadium1 == previous)
{
getline(csvFile2, iStadium2, ',');
getline(csvFile2, iDistance, '\n');
distance = stoi(iDistance);
index2 = 0;
found = false;
while(!found)
{
if(thisMap.atIndex(index2).value.getStadiumName() == iStadium2)
{
found = true;
cout << "Distance Size Test 2: " << thisMap.atIndex(index1).value.getDistanceSize() << endl;
// crashes here. Index out of bounds, size is 0 for some reason
thisMap.atIndex(index1).value.setDistance(index2, distance);
}
else
{
index2++;
}
}
getline(csvFile2, iStadium1, ',');
}
}
csvFile2.close();
}
I expect the vector to hold 30 slots (assuming the desired size passed into the function is 30) of value 0, rather than having an empty vector.

The code in your question works as expected after adding constructor and destructor (doing both nothing) :
#include <iostream>
#include <vector>
using namespace std;
class MLB
{
public:
//constructor
MLB();
~MLB();
int getDistanceSize();
void setInitialDistances(int size);
private:
vector<int> distances;
};
int MLB::getDistanceSize()
{
return distances.size();
}
void MLB::setInitialDistances(int size)
{
for(int i = 0; i < size; i++)
{
this->distances.push_back(0);
}
}
MLB::MLB() {
}
MLB::~MLB() {
}
int main()
{
MLB mlb;
mlb.setInitialDistances(30);
cout << mlb.getDistanceSize() << endl;
}
pi#raspberrypi:/tmp $ g++ d.cc
pi#raspberrypi:/tmp $ ./a.out
30
the vector is not empty but contains 30 times 0
if thisMap.atIndex(index1).value.setDistance(index2, distance); does nothing this is probably because atIndex(index1) returns a copy rather than a reference, so you modify a copy and the original is unchanged
For instance :
#include <iostream>
#include <vector>
using namespace std;
class C {
public:
vector<int> getv() { return v; } // return a copy
vector<int> & getvref() { return v; } // return the ref to the vector, not a copy
int len() { return v.size(); }
private:
vector<int> v;
};
int main()
{
C c;
c.getv().push_back(0); // modify a copy of v
cout << c.len() << endl;
c.getvref().push_back(0); // modify v
cout << c.len() << endl;
}
Compilation and execution :
pi#raspberrypi:/tmp $ g++ vv.cc
pi#raspberrypi:/tmp $ ./a.out
0
1
you edited you question and this is what I supposed :
entry Map::atIndex(int index)
{
return thisTable.at(index);
}
return a copy, must be
entry & Map::atIndex(int index)
{
return thisTable.at(index);
}

Related

Objects in Array are not being replaced by new Objects

This has been driving me insane for hours - I'm new to C++: I can't figure out why my programs thinks I want it do this.
I have a class House
class House{
private:
int number;
std::string family;
public:
House(int n, std::string f){
this->number = n;
this->family = f;
}
House(){
this->number = 0;
this->family = "unassigned";
}
void whoLivesHere(){
std::cout<<"The"<<family<<"lives here."<<std::endl;
}
};
I have another class Neighborhood
class Neighborhood{
private:
int size;
House houses[100];
public:
Neighborhood(){
this->size=0;
}
void addHouse(House h){
this->houses[this->size] = h;
this->size++;
}
void whoLivesHere(){
for(int i=0; i<this->size; i++){
this->houses[this->size].whoLivesHere();
}
}
};
And this is what is happening on my main.
int main(){
Neighborhood n1;
House h1(1,"Johnsons");
House h2(1,"Jones");
n1.addHouse(h1);
n1.addHouse(h2);
n1.whoLivesHere();
return 0;
}
And what I get on the Terminal is this.
The unassigned lives here
The unassigned lives here
The unassigned lives here
Why didn't the new objects replace the first two default objects?
Why show three objects? If size should be 1.
Thank you tonnes in advance!
You can make short work of this problem by using the tools the C++ Standard Library gives you, like this:
#include <string>
#include <vector>
#include <iostream>
int main() {
std::vector<House> neighborhood;
// emplace_back() forwards arguments to the constructor
neighborhood.emplace_back(1, "Johnson");
neighborhood.emplace_back(2, "Jones");
// No need to track size, std::vector does that for you: size(),
// but that's not even needed to iterate, you can just do this:
for (auto& house : neighborhood) {
house.whoLivesHere();
}
return 0;
}
Here I've cleaned up your House implementation:
class House {
private:
int number;
std::string family;
public:
// Tip: Use constructor lists
House(int n, const std::string& f) : number(n), family(f) { };
// Useful even for defaults
House() : number(0), family("unassigned") { };
// Flag methods that don't modify anything as const
void whoLivesHere() const {
std::cout << "The " << family << " lives here at number " << number << "." << std::endl;
}
};

Changing a value of an element in an object that is stored in a vector in another object through an external function in C++

So made a class called ‘Item’, and the object of that class will have a 100% condition at the start, the Player stores items (with name “apple” in this case) whenever I tell him to. In the degradeT function I want to pass the whole vector containing the items that the player has picked up by far and then change the condition of each Item in that vector by -1 through the chCond function.
first error:
initial value of reference to non-const must be an lvalue
second error:
'void degradeT(std::vector<Item,std::allocator<_Ty>> &)': cannot convert argument 1 from 'std::vector<Item,std::allocator<_Ty>>' to 'std::vector<Item,std::allocator<_Ty>> &'
#include "pch.h"
#include <iostream>
#include <string>
#include <vector>
using std::cout; using std::cin; using std::endl;
using std::string; using std::vector; using std::to_string;
class Item {
private:
string name; // Item name
float condition; // Item condition
bool consumable; // Is the item consumable
public:
Item() {}
Item(string a, float b, bool c) { name = a; condition = b; consumable = c; }
Item(string a, bool c) { name = a; condition = 100.f; consumable = c; }
string getName() {
return name;
}
float getCond() {
return condition;
}
bool isCons() {
return consumable;
}
void chCond(float a) { // Change Item condition
condition += a;
}
};
//-----------------------
class Player {
private:
vector<Item> plItems; // Item container
public:
Player() {}
void pickUpItem(Item a) { // Adding Items to inventory
plItems.push_back(a);
cout << a.getName() << " added to inventory!\n";
}
void checkItemConds() { // Checking condition of all items
for (unsigned int a = 0, siz = plItems.size(); a < siz; a++) {
cout << plItems[a].getName() << "'s condition is: " << plItems[a].getCond() << "%\n";
}
}
Item returnItem(unsigned int a) { // Return a specific Item
return plItems[a];
}
int getCurInvOcc() { // Get cuurent inventory occupation
return plItems.size();
}
vector<Item> getPlItems() { // Return the vector (Item container)
return plItems;
}
};
//-------------------------
void degradeT(vector<Item>& Itemss); // Degrade item after some time
//-------------------------
int main()
{
Player me; // me
string inp; // input
int num = 1; // apple 1, apple 2, apple 3...
while (inp != "exit") {
cin >> inp;
if (inp == "addApple") {
Item apple(("apple " + to_string(num)), true);
me.pickUpItem(apple);
num++;
}
if (inp == "checkItemConds") {
me.checkItemConds();
}
if (inp == "timeTick") {
// This doesn't have anything to do with time I just want to test the function manually
degradeT(me.getPlItems());
}
}
system("PAUSE");
return 0;
}
void degradeT(vector<Item> &Itemss) {
for (unsigned int a = 0, siz = Itemss.size(); a < siz; a++) {
Itemss[a].chCond(-1);
cout << Itemss[a].getName() << endl;
}
}
I'm not sure what your question is, but your error is related to the function void degradeT(vector<Item> & Itemss).
This functions expects a reference but you are passing an r-value. You can either return a reference with getPlItems() or pass an l-value to degradeT.

C++ MovieList array and pointer

I'm still a bit stuck on another part on my assignment.
Here is what the prompt is asking:
Now you can modify the LoadMovies function to create a MovieList
object and add each of the Movie objects to it. The function
LoadMovies should return a pointer to the MovieList object. That means
you need to create the MovieList object dynamically and on the heap.
Change the main function and store the returned MovieList pointer in a
variable. To test if everything works as expected, you can use the
PrintAll function of the MovieList object.
Here is my code so far:
class MovieList {
public:
Movie* movies;
int last_movie_index;
int movies_size;
int movie_count = 0;
MovieList(int size) {
movies_size = size;
movies = new Movie[movies_size];
last_movie_index = -1;
}
~MovieList() {
delete [] movies;
}
int Length() {
return movie_count;
}
bool IsFull() {
return movie_count == movies_size;
}
void Add(Movie const& m)
{
if (IsFull())
{
cout << "Cannot add movie, list is full" << endl;
return;
}
++last_movie_index;
movies[last_movie_index] = m;
}
void PrintAll() {
for (int i = 0; i < movie_count; i++) {
movies[last_movie_index].PrintMovie();
}
}
};
void ReadMovieFile(vector<string> &movies);
void LoadMovies();
enum MovieSortOrder
{
BY_YEAR = 0,
BY_NAME = 1,
BY_VOTES = 2
};
int main()
{
LoadMovies();
// TODO:
// You need to implement the Movie and MovieList classes and
// the methods below so that the program will produce
// the output described in the assignment.
//
// Once you have implemented everything, you should be able
// to simply uncomment the code below and run the program.
MovieList *movies = LoadMovies();
// // test methods for the Movie and MovieList classes
//PrintAllMoviesMadeInYear(movies, 1984);
//PrintAllMoviesWithStartLetter(movies, 'B');
//PrintAllTopNMovies(movies, 5);
//delete movies;
return 0;
}
void LoadMovies()
{
vector<string> movies;
ReadMovieFile(movies);
string name;
int year;
double rating;
int votes;
for (int i = 0; i < movies.size(); i++)
{
istringstream input_string(movies[i]);
getline(input_string, name, '\t');
input_string >> year >> rating >> votes;
Movie movie (name, year, votes, rating);
movie.PrintMovie();
}
}
Now where I'm stuck at is where the professor asks me to modify the LoadMovies in the prompt and turn it into a pointer. I'm drawing blanks. Also for some reason if I try to compile it says:
C:\Users\Andy\Documents\C++ Homework\MovieStatisticsProgram\MovieStatsProgram.cpp:163: error: void value not ignored as it ought to be
MovieList *movies = LoadMovies();
^
The order of your constructor is wrong
MovieList(int size) {
movies = new int[movies_size]; // movies_size hasn't been initialized yet!
movies_size = size;
last_movie_index = -1;
}
It should be
MovieList(int size)
: movies_size{size}, movies{new int[size]}, last_movie_index{0}
{}
Though as #ScottMcP-MVP noted your array should be
Movie* movie;
So your constuctor would be
MovieList(int size)
: movies_size{size}, movies{new Movie[size]}, last_movie_index{0}
{}
Some advice for getting started on the remaining functions
Length function will return how many are current used from last_movie_index.
IsFull will check if last_movie_index == movies_size - 1
Add will need to use last_movie_index to figure out what element in your array to store the movie.
PrintAll will have to iterate from [0] to [movie_count] and print out each element.
Your Add function would look something like
void MovieList::Add(Movie const& m)
{
if (IsFull())
{
std::cout << "Cannot add movie, list is full" << std::endl;
return;
}
movies[last_movie_index] = m; // assigns a copy to your array
++last_movie_index; // Increment the movie index
}

Fail to store values to the list

It seems the attribute test aisbn is successfully storing the data invoking setCode(), setDigit(). But The trouble starts failing while I attempt these values to store into list<test> simul
The list attribute takes the value of digit after setDigit() but the code. How can I put both code and digit into the list attribute? I can't see where the problem is. The code:
#include <iostream>
#include <stdlib.h>
#include <string>
#include <fstream>
#include <list>
using namespace std;
class test
{
private:
string code;
int digit;
public:
//constructor
test(): code(""), digit(0) { }
//copy constructor
test(const test &other):
digit(other.digit)
{
for(unsigned int i=0; i < code.length(); i++)
code[i] = other.code[i];
}
//set up the private values
void setCode(const string &temp, const int num);
void setCode(const string &temp);
void setDigit(const int &num);
//return the value of the pointer character
const string &getCode() const;
const unsigned int getDigit() const;
};
const string& test::getCode() const
{
return code;
}
const unsigned int test::getDigit() const
{
return digit;
}
void test::setCode(const string &temp, const int num)
{
if((int)code.size() <= num)
{
code.resize(num+1);
}
code[num] = temp[num];
}
void test::setCode(const string &temp)
{
code = temp;
}
void test::setDigit(const int &num)
{
digit = num;
}
int main()
{
const string contents = "dfskr-123";
test aisbn;
list<test> simul;
list<test>::iterator testitr;
testitr = simul.begin();
int count = 0;
cout << contents << '\n';
for(int i=0; i < (int)contents.length(); i++)
{
aisbn.setCode(contents);
aisbn.setDigit(count+1);
simul.push_back(aisbn);
count++;
}
cout << contents << '\n';
/*for(; testitr !=simul.end(); simul++)
{
cout << testitr->getCode() << "\n";
}*/
}
It looks like you are having issues with your for loop, you need to modify your for loop like so:
for(testitr = simul.begin(); testitr !=simul.end(); testitr++)
^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^
although, push_back does not invalidate iterators for std::list I think it is more readable to set the iterator where you are using it. Based on your response you also need to modify the copy constructor:
test(const test &other): code(other.code), digit(other.digit) {}
^^^^^^^^^^^^^^^^
how about using the vector
std::vector<test> simul;
for(int i=0; i < (int)contents.length(); i++)
{
aisbn.setCode(contents);
aisbn.setDigit(count+1);
simul.push_back(aisbn);
count++;
}
iterators, pointers and references related to the container are invalidated.
Otherwise, only the last iterator is invalidated.

Unresolved overloaded type>[int] for array subscript c++

I'm getting the error message 'Unresolved overloaded type>[int] for array subscript' in my flight-booking-system program.
What I'm trying to do is set it so that if [j] is equal to 0,1,2,3... it will display accordingly as A,B,C,D. Until I started doing this my program at least compiled。
// Flight Class - Scotia 2
//
// Contains information on seating (array), space available and return to menu option.
#include <iostream>
#include <string>
#include "passenger.h"
#include "Seat.h"
using namespace std;
/*struct Seat
{
int Available;
std::string fullName;
};// End of struct*/
class Flight
{
public:
//default constructor
Flight()
{
//initialise all seat numbers
for(int i=0;i<4;i++)
for(int j=0;j<6;j++)
{// assigns seats as 1A, 1B etc...
seatPlan[i][j].setRow(row);
if(j==0)
seatPlan[i][j].setCol('A');
else if(j==1)
seatPlan[i][j].setCol('B');
else if(j==2)
seatPlan[i][j].setCol('C');
else if(j==3)
seatPlan[i][j].setCol('D');
}
}
Seat seatArray[4][6];
void seatPlan()
{
for (int ROW=0;ROW<4;ROW++)
{
for (int COL=0;COL<6;COL++)
{
cout << seatPlan[i][j].getSeatRow();
}
}
// End of for loop
}// End of seatPlan function
//method which returns true if seat is Available and false otherwise
bool getAvailable(int i, int j)
{
if(seatArray[i][j].Available == 0)
return true; //seat available
else
return false; //seat occupuied
}
string getName(int i,int j){return seatArray[i][j].fullName;}
void setAvailable(int i, int j, int a){seatArray[i][j].Available = a;}
void setName(int i,int j, string name){seatArray[i][j].fullName = name;}
private:
//variables
int row;
char col;
};// End of Flight class
The above is my flight.h file which contains the Flight class. The error message points to my constructor, with the message repeating for all the lines within that contain seatPlan[i][j].setCol('A'); and so on.
I'll include the 'seat.h' file also, just in case it's relevant.
#ifndef SEAT
#define SEAT
#include <iostream>
using namespace std;
class Seat
{
public:
//deafult constructor
Seat(){available = true;}
//accessor methods
void setRow(int row){seatRow = row;}
void setCol(char col){seatCol = col;}
int getSeatRow(){return seatRow;}
char getSeatCol(){return seatCol;}
bool isAvailable(){return available;}
bool switchAvailable(){
if(available)
available = false;
else
available = true;
}
private:
bool available;
int seatRow;
char seatCol;
};
#endif
seatPlan[i][j].setRow(row);
Here is the problem. seatPlan is not an array. It is the name of the function.
You meant seatArray. So it should be:
seatArray[i][j].setRow(row);
One suggestion: consider using std::array as:
std::array<std::array<Seat,6>,4> seatArray;
instead of
Seat seatArray[4][6];
void seatPlan() is a method and you're treating it as an array. Did you mean seatArray instead?
Also
if(seatArray[i][j].Available == 0)
return true; //seat available
else
return false; //seat occupuied
? Really? Why not just
return seatArray[i][j].Available == 0;
(assuming you fix the previous error)