I am creating a vector that contains pointers to a base class. In this vector I'm dynamically storing pointers to derived classes which contain some member variables, one of them being a string variable name.
#include "stdafx.h"
#include <iostream>
#include <vector>
#include <string>
#include <cstdlib>
bool hasDirection = false;
bool hasDiameter = false;
int direction;
float diameter;
int starDimension = 0;
int animalDimension = 0;
int fishDimension = 0;
class MovingObject
{
protected:
std::string name;
int direction;
float diameter;
int dimension;
float movingSpeed;
public:
std::string getName(){ return name;};
int getDirection(){ return direction;};
float getDiameter(){ return diameter;};
float getMovingSpeed(){ return movingSpeed;};
int getDimension(){ return dimension;};
void setName(std::string v){ name = v;};
void setDirection(int d){ direction = d;};
void setDiameter(float f){ diameter = f;};
void setMovingSpeed(float s){ movingSpeed = s;};
void setDimension (int d){ dimension = d;};
virtual void PrintContents()=0;
};
static std::vector<MovingObject*> data;
class starObject : public MovingObject
{
public:
void PrintContents()
{
std::cout << "(" << getName() << "," << getDiameter() << "," << getDirection() << ")";
}
};
class animalObject : public MovingObject
{
public:
void PrintContents()
{
std::cout << "(" << getName() << "," << getDiameter() << "," << getDirection() << ")";
}
};
class fishObject : public MovingObject
{
public:
void PrintContents()
{
std::cout << "(" << getName() << "," << getDiameter() << "," << getDirection() << ", [" << getDimension() << "], " << getMovingSpeed() << ")";
}
};
I later set all these member variables inside a main function. The problem is when I try to output the contents of the member variables, all of them show up except for the string name.
Now, I've checked to make sure that the string gets set before calling the PrintContent() method, and it shows that the value is in the vector. However, when I debug through the code, the value is no longer there, instead containing an empty string.
Could someone with better c++ knowledge explain to me why this is happening? This is the main class:
int main()
{
std::string type;
Reader reader;
while (!std::cin.eof())
{
try
{
std::string type;
std::cin >> type;
if (type =="int")
{
reader.ReadDirection();
}
else if (type =="float")
{
reader.ReadDiameter();
}
else if (type == "string")
{
std::string name;
std::cin >> name;
if (hasDirection && hasDiameter)
{
int dimension;
if (diameter > 0 && diameter < 10)
{
//fish
fishObject fish;
fish.setName(name);
fish.setDiameter(diameter);
fish.setDirection(direction);
dimension = fishDimension;
fishDimension += 50;
fish.setDimension(dimension);
fish.setMovingSpeed(0.1);
data.push_back(&fish);
}
else if (diameter >= 10 < 500)
{
//animal
animalObject animal;
animal.setName(name);
animal.setDiameter(diameter);
animal.setDirection(direction);
dimension = animalDimension;
animalDimension += 800;
animal.setDimension(dimension);
animal.setMovingSpeed(5.0);
data.push_back(&animal);
}
else if (diameter >=500)
{
//star
starObject star;
star.setName(name);
star.setDiameter(diameter);
star.setDirection(direction);
dimension = starDimension;
starDimension += 5000;
star.setDimension(dimension);
star.setMovingSpeed(30.0);
data.push_back(&star);
}
}
else
{
throw (IncompleteData(name));
}
}
}
catch (IncompleteData e)
{
std::cerr << "No diameter or direction given for object " << e.objectName << "\n";
}
}
The objects you push to the data vector are local because they are declared inside if/else blocks (see the declarations of fish and animal).
When you push the address of such an object to the vector, it will continue to point to the local object, which ceases to exist at the end of the local scope. You need to create objects that live beyond the local scope. One way of doing this is to create copies of the local objects on the heap and push those to the vector:
data.push_back(new fishObject(fish));
Of course this means that you get a memory leak unless you make sure you explicitly delete the elements of the vector some time before the end of the program. The usual recommendation to avoid having to think of this is to use a vector of std::unique_ptr<MovingObject> instead of a vector of naked pointers.
Related
I am trying to create a program that uses class, arrays, and functions to show information about two students(Name, id#, classes registered). The part I am struggling with is passing arrays to a function. How do I do that?
#include <string>
#include <iostream>
#include <iomanip>
using namespace std;
class Student // Student class declaration.
{
private:
string name;
int id;
string classes;
int arraySize;
public:
void setName(string n)
{
name = n;
}
void setId(int i)
{
id = i;
}
void setClasses(string c, int num)
{
classes = c;
arraySize = num;
}
string getName()
{
return name;
}
int getId()
{
return id;
}
void getClasses()
{
for (int counter=0; counter <arraySize; counter++) {
cout << classes[counter] << endl;
}
}
};
int main()
{
//Student 1
string s1Name = "John Doe";
int s1Id = 51090210;
int const NUMCLASSES1 = 3;
string s1Classes[NUMCLASSES1] = {"C++","Intro to Theatre","Stagecraft"};
//Student 2
string s2Name = "Rick Harambe Sanchez";
int s2Id = 666123420;
int const NUMCLASSES2 = 2;
string s2Classes[NUMCLASSES2] = {"Intro to Rocket Science","Intermediate Acting"};
//
Student info;
info.setName(s1Name);
info.setId(s1Id);
//info.setClasses(s1Classes, NUMCLASSES1);
cout << "Here is Student #1's information:\n";
cout << "Name: " << info.getName() << endl;
cout << "ID: " << info.getId() << endl;
//cout << "Classes: " << info.getClasses() << endl;
info.setName(s2Name);
info.setId(s2Id);
// info.setClasses(s2Classes, NUMCLASSES1);
cout << "\n\nHere is student #2's information:\n";
cout << "Name: " << info.getName() << endl;
cout << "ID: " << info.getId() << endl;
//cout << "Classes: " << info.getClasses() << endl;
return 0;
}
The usual way to pass around variable-length lists in C++ is to use an std::vector. A vector is a single object that you can easily pass to a function, copying (or referencing) its contents. If you are familiar with Java, it's basically an ArrayList. Here is an example:
#include <vector>
#include <string>
using namespace std;
class foo {
private:
vector<string> myStrings;
public:
void setMyStrings(vector<string> vec) {
myStrings = vec;
}
}
//...
foo myObj;
vector<string> list = {"foo","bar","baz"};
myObj.setMyStrings(list);
If don't want to use the standard library though, you can pass an array C-style. This involves passing a pointer to the first element of the array, and the length of the array. Example:
void processStrings(string* arr, int len) {
for (int i = 0; i < len; i++) {
string str = arr[i];
//...
}
}
string array[] = {"foo","bar","baz"};
processStrings(array, 3); // you could also replace 3 with sizeof(array)
Passing raw arrays like this, especially if you wanted to then copy the array into an object, can be painful. Raw arrays in C & C++ are just pointers to the first element of the list. Unlike in languages like Java and JavaScript, they don't keep track of their length, and you can't just assign one array to another. An std::vector encapsulates the concept of a "list of things" and is generally more intuitive to use for that purpose.
Life lesson: use std::vector.
EDIT: See #nathanesau's answer for an example of using constructors to initialize objects more cleanly. (But don't copy-paste, write it up yourself! You'll learn a lot faster that way.)
You can pass array of any_data_type to function like this
void foo(data_type arr[]);
foo(arr); // If you just want to use the value of array
foo(&arr); // If you want to alter the value of array.
Use std::vector. Also, don't add functions you don't need. Here's an example of using std::vector
#include <string>
#include <iostream>
#include <vector>
using std::string;
using std::vector;
class Student // Student class declaration.
{
private:
vector<string> classes;
string name;
int id;
public:
Student (const vector<string> &classesUse, string nameUse, int idUse) :
classes (classesUse),
name (nameUse),
id (idUse)
{
}
void print ()
{
std::cout << "Name: " << name << std::endl;
std::cout << "Id: " << id << std::endl;
std::cout << "Classes: ";
for (int i = 0; i < classes.size (); i++)
{
if (i < classes.size () - 1)
{
std::cout << classes[i] << ", ";
}
else
{
std::cout << classes[i] << std::endl;
}
}
std::cout << std::endl;
}
};
int main()
{
Student John ({"C++","Intro to Theatre","Stagecraft"},
"John",
51090210);
John.print ();
Student Rick ({"Intro to Rocket Science","Intermediate Acting"},
"Rick",
666123420);
Rick.print ();
return 0;
}
Name: John
Id: 51090210
Classes: C++, Intro to Theatre, Stagecraft
Name: Rick
Id: 666123420
Classes: Intro to Rocket Science, Intermediate Acting
In the private variables of class Student, you are storing a string:
String classes;
where as you should be storing an array of strings like:
String classes[MAX_NUM_CLASSES];
then in the set classes function, pass in an array of strings as the first argument, so it should be :
void setClasses(string[] c, int num)
{
classes = c; //not sure if simply setting them equal will work, rather copy entire array using a for loop
arraySize = num;
}
This should point you in the right direction
Also, use std::vector instead of string[], it will be easier.
I have a problem where I have 2 classes, Word and Noun. Noun is derived from Word.
All Words and Nouns are to be stored in a single vector hence why I require it being in pointer.
The problem is I can't seem to initialize or call functions from the derived class Noun.
I can pushback for a new Word but not for a Noun.
#include "stdafx.h"
#include <iostream>
#include <string>
#include <vector>
using namespace std;
class Word{
protected:
string wordName, def, type;
public:
Word();
Word(string wordName, string def, string type) {
this->wordName = wordName;
this->def = def;
this->type = type;
};
void getWord() {
cout << wordName << endl;
}
void getDef() {
cout << def << endl;
}
void getType() {
cout << type << endl;
}
};
class Noun : public Word{
public:
Noun();
Noun(string wordName, string type, string def);
};
int main(){
vector <Word*> wordVector;
for (int i = 0; i < 2; i++)
{
string wordName, def, type;
cin >> wordName;
cin >> def;
cin >> type;
cout << endl;
wordVector.push_back(new Noun(wordName, def, type)); //new Word(wordName, def, type) works
}
for (int i = 0; i < 2; i++)
{
wordVector[i]->getWord(); //how do you call the function from Noun?
wordVector[i]->getDef();
wordVector[i]->getType();
}
system("pause");
return 0;
}
It comes out with 1 unresolved external symbol.
There are too many things wrong with this code, so allow me to present a correct, complete rewrite that does what you mean:
#include <iostream>
#include <memory> // for std::unique_ptr
#include <string>
#include <vector>
class Word
{
private:
std::string wordName, def, type;
public:
virtual ~Word() = default;
Word(std::string w, std::string d, std::string t)
: wordName(std::move(w))
, def(std::move(d))
, type(std::move(t)) {}
void printWord() const { std::cout << wordName << '\n'; }
void printDef() { std::cout << def << '\n'; }
void printType() const { std::cout << type << '\n'; }
};
class Noun : public Word
{
public:
using Word::Word;
};
int main()
{
std::vector<std::unique_ptr<Word>> wordVector;
for (int i = 0; i != 2; ++i)
{
std::string w, d, t;
if (!(std::cin >> w >> d >> t))
{
std::cerr << "Failed to read input!\n";
continue;
}
wordVector.push_back(std::make_unique<Noun>(
std::move(w), std::move(d), std::move(t)));
}
for (const auto& wp : wordVector)
{
wp->printWord();
wp->printDef();
wp->printType();
}
}
A completely unsorted and incomplete set of issues that I corrected:
Memory management (std::unique_ptr)
Virtual destructor for deletion through base
No nonsensical default constructors
Inheriting constructors rather than manual forwarding
Properly named member functions
Const correctness
No superfluous semicolons
No superfluous std::endl
Not abusing namespace std
Range-based for loop
I/O error handling
Initialize rather than assign
Enable move optimizations
No raw new
Correct access level for private members (exposed via member functions)
I think you just forgot to initialize the superclass constructor In your Noun class try this
class Noun : public Word{
public:
Noun();
Noun(string wordName, string type, string def): Word(wordName, type, def){};
};
I have tested it and it worked.
Also theres a light modification in you main(). just a slight. so that i can see what input it is asking for.
int main(){
vector <Word*> wordVector;
for (int i = 0; i < 2; i++)
{
string wordName, def, type;
cout<< "entere name";
cin >> wordName;
cout<< "entere def";
cin >> def;
cout<< "entere type";
cin >> type;
cout << endl;
wordVector.push_back(new Noun(wordName, def, type)); //new Word(wordName, def, type) works
}
for (int i = 0; i < 2; i++)
{
wordVector[i]->getWord(); //how do you call the function from Noun?
wordVector[i]->getDef();
wordVector[i]->getType();
}
system("pause");
return 0;
}
This question already has answers here:
Can a local variable's memory be accessed outside its scope?
(20 answers)
Closed 7 years ago.
I have been attempting to create a function getLocation() that utilizes a pointer to return the value of the struct Location declared in the Character class. I was curious as to the problem with my syntax (or my structure). Knowing that the asterisk * should refer to the value, why is it that my function using an ampersand string& Character::getInventory is able to return the value of that particular index (its return does not need to be converted)?
Trying Location& Character::getLocation() {return position; }
when run results in error C2679: binary '<<': no operator found
Nor
Location*
Which cannot be run as there is no conversion.
I read that the following is likely the most proper because it specifies the scope in which the structure resides, but still results in needing and returning a temporary.
Character::Location* const & Character::getLocation() {return &position; }
Any advice or input would be greatly appreciated, thanks in advance.
Below is my main.cpp, which of course will show the hexadecimal address for Location.
#include <iostream>
#include <string>
using std::cerr;
using std::cin;
using std::cout;
using std::endl;
using std::string;
class Character {
private:
string name;
string inventory[4];
public:
struct Location {
int x; int y;
};
Location position;
public:
void Character::setName(string x) { name = x; }
string Character::getName() { return name; }
void Character::setLocation(int x, int y) {
position.x = x; position.y = y;
}
Location* Character::getLocation() {return &position; }
void Character::setInventory(string(&x)[4]) { for (int i = 0; i < 4; ++i) { inventory[i] = x[i]; } }
string& Character::getInventory(int itemNumber) { return inventory[itemNumber]; }
};
void showUser(Character Character);
int main() {
try {
string items[4] = { "Sword", "Shield", "Potion", "Cloak" };
Character CharacterI;
CharacterI.setName("Some Character");
CharacterI.setInventory(items);
CharacterI.setLocation(1, 30);
cout << "\n" << "Retrieving Character Info..." << "\n" << endl;
showUser(CharacterI);
}
catch (std::exception & e) {
cerr << "\nError : " << e.what() << '\n';
}
system("pause");
return 0;
}
void showUser(Character character) {
cout << "Name : " << character.getName() << endl;
cout << "Location : " << character.getLocation() << endl;
for (int i = 0; i < 4; ++i) {
cout << "Inventory " << i + 1 << " : " << character.getInventory(i) << endl;
}
}
Ok, I think I understand the question better now. The reason why getInventory can successfully return a reference while getLocation does not is because getLocation returns a reference to a temporary variable, which is not good. See the link in #NathanOliver's comment for details. Additionally, to paraphrase a previous comment by #Peter Schneider, an * in an expression dereferences a pointer to return a value, while in a declaration it signifies that a variable will be of pointer type. The two usages are more or less opposites of each other. Example:
int* p = new int; //Declares a pointer to int
int x = *p; //Dereferences a pointer and returns an int
What you need to do is create a member variable to hold the Character's location, then set/get from that variable instead of creating temporaries. You did this already for name and inventory, just keep using that same pattern.
Additionally, whenever you use the Location struct outside of the Character class scope, you need to fully-qualify it with Character::Location.
Example:
#include <iostream>
using namespace std;
class Character {
public:
struct Location {
int x;
int y;
};
Location loc;
void SetLocation(int x, int y) {loc.x = x; loc.y = y;}
Location& GetLocation() {return loc;}
};
int main ()
{
Character c;
c.SetLocation(1,42);
Character::Location l = c.GetLocation();
cout << l.x << endl << l.y << endl;
return 0;
}
Output:
1
42
I have a Spieler class and a Verein class with a vector of Spieler members.
Now if I change something of the Players like the Staerke(german for strength) by using a function of this class in the player class it does not automatically change the value for this player.
Here is the code:
#include <vector>
#include<iostream>
#include <string>
using namespace std;
class Spieler
{
public:
void setinformation(int a, string b, string c, int d)
{
ID = a;
Vorname = b;
Nachname = c;
Staerke = d;
}
void getinformation()
{
cout << "ID: " << ID << endl;
cout << "Vorname: " << Vorname << endl;
cout << "Nachname: " << Nachname << endl;
cout << "Staerke: " << Staerke << endl << endl;
}
void setStaerke(int x)
{
Staerke = x;
}
int getStaerke()
{
return Staerke;
}
private:
string Vorname, Nachname;
int Staerke, ID;
};
class Verein
{
public:
void setSpielerListe(vector<Spieler> x)
{
Spielerliste = x;
}
vector<Spieler> getSpielerListe()
{
return Spielerliste;
}
string getVereinsName()
{
return VereinsName;
}
int getVereinsID() const
{
return VereinsID;
}
void setVereinsID(int x)
{
VereinsID = x;
}
int getGesamtstaerke()
{
Gesamtstaerke = 0;
vector<Spieler> b;
b = getSpielerListe();
for (size_t i = 0; i < b.size(); i++)
{
Gesamtstaerke = Gesamtstaerke + b[i].getStaerke();
}
return Gesamtstaerke;
}
void Vereinsinformationen()
{
vector<Spieler> list;
int id;
string vereinsname;
int gesamtstaerke;
id = getVereinsID();
vereinsname = getVereinsName();
gesamtstaerke = getGesamtstaerke();
list = getSpielerListe();
cout << "VereinsID: " << id << endl;
cout << "Vereinsname: " << vereinsname << endl;
cout << "Gesamstaerke: " << gesamtstaerke << endl << endl;
cout << "Spieler: " << endl;
for (size_t i = 0; i < list.size(); i++)
list[i].getinformation();
}
private:
vector<Spieler> Spielerliste;
int VereinsID, Gesamtstaerke;
string VereinsName;
};
vector<Spieler> spieler;
int main()
{
Spieler Spieler1;
Spieler1.setinformation(0, "Peter", "Pan", 10);
spieler.emplace_back(Spieler1);
Verein Team1;
Team1.setSpielerListe(spieler);
Spieler1.setStaerke(20);
Team1.Vereinsinformationen();
cin.get();
return 0;
}
I'm really new into c++ and programming so the code might be terrible.
Guess it has to do with pointers, I'm really not into the concept of storing data in c++, try to get it by trial & error; So how to change the Staerke in a way that it is changed in the Teams Playerlist too?
The problem is you are storing full object in the vector and not pointers. When you run this line:
spieler.emplace_back(Spieler1);
a copy of Spieler1 is made and put in the vector. So modifying it in the main will have no effect in the vector. Also not that you are copying the vector when setting in Verein class.
You should use pointer if this is what you are after or better yet have a function to modify strength from Verein class taking its id and new strength as parameters might be a good idea. Something like this:
void setStaerke(int id, int x)
{
vector<Spieler>::iterator it = Spielerliste.begin();
while (it != Spielerliste.end())
{
if ((*it).GetId() == id)
{
(*it).setStaerke(x);
break;
}
}
}
If you have access to C++11, it could be made more elegantly.
Hereby you pass and store a copy from the vector into the object:
Team1.setSpielerListe(spieler);
Therefore changes to the original vector and the contained objects will not affect the member.
Further, I don't have much experience with emplace_back, but the more usual way to append an object to a std::vector would also append a copy:
spieler.push_back(Spieler1);
Therefore changes to the original object would not affect the object you've appended to the container.
Make sure you better understand when objects are copied.
For reference:
http://en.cppreference.com/w/cpp/container/vector/emplace_back
http://en.cppreference.com/w/cpp/container/vector/push_back
How to pass objects to functions in C++?
I have the following code written in C++:
#include<iostream>
#include<vector>
using namespace std;
class cViews {
string viewName;
double minD;
vector<double> dss;
public:
string minInput1, minInput2;
cViews(string);
cViews();
void setName(string s) { viewName = s; }
string getName() { return viewName; }
void setMinI(string m) { minInput1 = m; }
string getMinI() { return minInput1; }
void setMinD(double d) { minD = d; }
double getMinD() { return minD; }
void addD(vector<double> k){ dss = k; }
vector<double> getD(){ return dss; }
};
cViews::cViews(string str) {
viewName = str;
vector<double> dss = vector<double>();
}
cViews::cViews() {
vector<double> dss = vector<double>();
}
class Obj{
string name;
cViews dist;
public:
Obj(string);
void setName(string s) { name = s; }
string getName() { return name; }
void addDist(cViews k){ dist = k; }
cViews getDist(){ return dist; }
};
Obj::Obj(string str) {
name = str;
cViews dist();
}
void changeViewN(cViews *v, string s){
v->setMinI(s);
}
int main(){
Obj o1("Object1");
cViews v3;
cViews v1("View 1");
v1.setMinI("View 2");
v1.setMinD(1);
o1.addDist(v1);
cout << o1.getName() << " " << o1.getDist().getMinI() << endl;
v3 = o1.getDist();
changeViewN(&v3, "Changed");
cout << o1.getName() << " " << o1.getDist().getMinI() << endl;
return 0;
}
Output is:
Object1 View 2
Object1 View 2
The problem here is I am trying to change the value of an object that was created within another object.
Output should be:
Object1 View 2
Object1 Changed
Any help is greatly appreciated. Thank you.
To change the object and not a copy, ou have to use pointers or references. Else you just copy the object returned from getDist() and thus cant change the original object.
cViews* getDist(){ return &dist; }
...
changeViewN(o1.getDist(), "Changed");
It seems you got a couple of problems, the first few:
cViews::cViews(string str) {
vector<double> dss = vector<double>();
}
viewName isn't initialized, dss is Declared in the function (which is meaningless as it will be scrapped as soon as the function returns).
ps. you would like to change the second line like this:
cout << o1.getName() << " " << o1.getDist().getMinI() << endl;
to
cout << o2.getName() << " " << o2.getDist().getMinI() << endl;
You should really proofread your code ...