OOP: Method for cout output - c++

I have to create a method, which prints all collected data's on screen, here is my try:
bool UnPackedFood::printer() {
cout << " -- Unpacked Products --" << endl;
cout << "barcode: " << getBarcode() << endl;
cout << "product name: " << getBezeichnung() << endl << endl;
cout << "weight: " << getGewicht() << endl;
cout << "price" << getKilopreis() << endl;
return true;
}
In my main:
UnPackedFood upf;
cout << upf.printer();
This shows me the correct output, but it still delivers me a bool value back, which I actually dont need. I tried to declare the method as void, but thats not working.

You should overload << operator for output stream. Then when you type cout << upf it will print your product.
Take a look at this example and try to do something similar to following snippet:
class UnPackedFood {
...
public:
...
friend ostream & operator<< (ostream &out, const UnPackedFood &p);
};
ostream & operator<< (ostream &out, const UnPackedFood &p) {
out << " -- Unpacked Products --" << endl;
out << "barcode: " << p.getBarcode() << endl;
out << "product name: " << p.getBezeichnung() << endl << endl;
out << "weight: " << p.getGewicht() << endl;
out << "price" << p.getKilopreis() << endl;
return out;
}

Three possible solutions:
Don't do cout << upf.printer();, the output is not needed since the function itself does the output.
Instead of writing to the output in the printer function, append to a string and return the string.
Make an overloaded operator<< for UnPackedFood, so you can just do std::cout << upf;

Related

C++ access object behind iterator in loop

I have created a list of objects of a class.
The class has an overloaded ostream << operator to output customer data in a structured way.
What I am trying to do is loop over the list of objects and call cout on the object in the iteration.
Code for the loop is as follows:
for (list<Kunde>::iterator it = this->kun_list.begin(); it != this->kun_list.end(); ++it) {
cout << it << endl;
}
With Kunde being the class with the overloaded << operator and kun_list being the list of objects of type Kunde.
friendly overload within the Kunde class:
friend ostream& operator<< (ostream& os, Kunde& kd) {
os << "__Kundendaten__" << endl;
os << "Name: " << kd.vorname << " " << kd.name << endl;
os << "Geburtsjahr: "<< kd.geburtsjahr << endl;
os << "Adresse: " << kd.strasse << " " << kd.hausnummer << endl << kd.plz << " " << kd.ort << endl;
os << "Telefon: " << kd.telefonnummer << endl;
string fschein = "Nein.";
if (kd.klasse_a_vorhanden) {fschein = "Ja.";}
os << "Führerschein Kl. A vorhanden: " << fschein << endl;
return os;
};
The above loop does not work because I am using the list iterator instead of an object of class Kunde. I can access members of Kunde via it→member but how do I use that iterator as reference to the whole object?
Thanks!
Use a const reference loop over the container:
for (const auto & kunde : kun_list) {
cout << kunde << endl;
}
Obviously you also have to fix <<:
friend ostream& operator<< (ostream& os, const Kunde& kd) {...}

C++ proper usage of ostream inside a class and passing arguments?

I've recently started learning c++ and for the life of me, I can't seem to get the syntax of using ostream in a class and what arguments should I pass. Here's the code:
This is the class in question:
#include <iostream>
#include <string>
using namespace std;
class Pokemon{
friend ostream& operator<<(ostream&, Pokemon);
public:
string name, level, cp;
Pokemon(string x="Pikachu", string y="5", string z="1000"){
name = x;
level = y;
cp = z;
}
Pokemon name(){
return this->name;
}
Pokemon level(){
return this->level;
}
Pokemon cp(){
return this->cp;
}
Pokemon display_stats(){
cout << this-> name << "stats are:" << endl;
cout << " " << "Attack: 2716.05" << endl;
cout << " " << "Defence: 1629.63" << endl;
cout << " " << "HP: 1086.42" << endl;
}
};
template<typename TYPE> //i dont understand this and the things i've written down here are only based on samples i've seen
ostream& operator<<(ostream& os, Pokemon & c){
os << "The level of " << c.name << " is" << c.level << " with cp of " << c.cp;
}
As you could see, I already tried constructing the ostream thing but I don't really understand how it works. This is my main function:
int main()
{
Pokemon a, b, c, d;
a = Pokemon();
b = Pokemon("Weezing");
c = Pokemon("Nidoking", 100);
d = Pokemon("Mewtwo", 50, 5432.1);
cout << a << endl;
cout << b << endl;
cout << c << endl;
cout << d << endl;
cout << "Jessie: You are no match to me! Go " << b.name << "!" << endl;
cout << "Gary: Go lvl " << c.level << " " << c.name << "! Crush them" << endl;
cout << "Ash: " << a.name << " can do it even thouh he is only level " << a.level << endl;
cout << "Jessie: Hahaha! My " << b.name << " CP is " << b.cp << endl;
cout << "Gary: "<< c.name << " CP is " << c.cp << endl;
cout << "Ash: " << a.name << " CP is " << a.cp << endl;
cout << "Giovanni: Behold " << d.name << " is here." << endl;
d.display_stats();
return 0;
}
I'm getting errors of:
no instance of constructor "Pokemon::Pokemon" matches the argument list -- argument types are: (const char [9], int) //on line c = Pokemon("Nidoking", 100);
no instance of constructor "Pokemon::Pokemon" matches the argument list -- argument types are: (const char [7], int, double) //on line d = Pokemon("Mewtwo", 50, 5432.1);
All of your Pokemon class methods are returning the wrong type. And your main() is not calling any of the methods correctly at all.
Change your Pokemon class to look more like this:
#include <iostream>
#include <string>
using namespace std;
class Pokemon {
private:
string m_name;
int m_level;
double m_cp;
friend ostream& operator<<(ostream&, const Pokemon&);
public:
Pokemon(string x="Pikachu", int y=5, double z=1000) {
m_name = x;
m_level = y;
m_cp = z;
}
string name() const {
return m_name;
}
int level() const {
return m_level;
}
double cp() const {
return m_cp;
}
void display_stats() const {
cout << m_name << " stats are:" << endl;
cout << " " << "Attack: 2716.05" << endl;
cout << " " << "Defense: 1629.63" << endl;
cout << " " << "HP: 1086.42" << endl;
}
};
ostream& operator<<(ostream& os, const Pokemon &c) {
os << "The level of " << c.m_name << " is " << c.m_level << " with cp of " << c.m_cp;
return os;
}
And then change main() to look more like this:
int main()
{
Pokemon a;
Pokemon b("Weezing");
Pokemon c("Nidoking", 100);
Pokemon d("Mewtwo", 50, 5432.1);
cout << a << endl;
cout << b << endl;
cout << c << endl;
cout << d << endl;
cout << "Jessie: You are no match to me! Go " << b.name() << "!" << endl;
cout << "Gary: Go lvl " << c.level() << " " << c.name() << "! Crush them" << endl;
cout << "Ash: " << a.name() << " can do it even though he is only level " << a.level() << endl;
cout << "Jessie: Hahaha! My " << b.name() << " CP is " << b.cp() << endl;
cout << "Gary: " << c.name() << " CP is " << c.cp() << endl;
cout << "Ash: " << a.name() << " CP is " << a.cp() << endl;
cout << "Giovanni: Behold " << d.name() << " is here." << endl;
d.display_stats();
return 0;
}
Live Demo

Use of ostream_iterator with an auto type?

In my college exam preparation I'm supposed to use ostream_operator with "auto" keyword.
Below is what I tried but the "auto" word is underlined in red with the error stating that `auto is not allowed here'.
I need auto here because the class attribute within the vector are of another class' type and is not recognized from within this current class.
ostream& operator<<(ostream& COUT, const Nastava& obj)
{
COUT << "<" << obj._datum << " - " << obj._satnica << "> <" << obj._prostorija << "> " << " <" << obj._predavac << "> " << obj._tipNastave;
COUT << endl << obj._predmet->Info();
ostream_iterator<auto> outit(COUT, "\n");
copy(obj._prisutni->begin(), obj._prisutni->end(), outit);
return COUT;
}

C++ no operator "<<" match these operand (inheritance)

I have just recently started class inheritance in c++. While I was making a "Test" program, a error occurred with the cout statement. No clue how to fix it and would be appreciate your response.
#include <iostream>
using namespace std;
class Power{
public:
void isWeak(){
cout << " Weak"<< endl;
}
void isStrong(){
cout << " Strong" << endl;
}
};
class Person:public Power{};
class Person2:public Power{};
int main(){
Person human;
Person2 human2;
cout << "Human is " << human.isWeak() << endl; //error
cout << "Human 2 is " << human2.isStrong() << endl; //error
system("pause");
return 0;
}
the main()'s cout statement has that error between the output and human
Change the functions to
char const *isWeak(){
return " Weak";
}
char const *isStrong(){
return " Strong";
}
As currently defined, both functions have void return type, which means the cout statements within main are trying to print void, which doesn't make sense, and is the cause of the error.
You are attempting to print a void:
cout << "Human is " << human.isWeak() << endl;
is the same as typing
cout << "Human is " << void << endl;
Which will not compile. What you need to do is define your functions in either of the following ways:
class Power
{
public:
std::string isWeak()
{
return std::string(" is weak");
}
std::string isStrong()
{
return std::string(" is strong");
}
};
Or, change your code:
cout << "Human is ";
human.isWeak();
cout << endl;
cout << "Human 2 is ";
human2.isStrong();
cout << endl;
Problem is with isWeak() and isStrong() return type. these two functions return void and you are trying to print it. you can try this-
cout << "Human is " ;
human.isWeak();
cout << endl;
cout << "Human 2 is " ;
human2.isStrong();
cout << endl;
You're trying to 'print' a 'void' statement in cout << "Human is " << human.isWeak() << endl;
You'll need to change your isWeak and isStrong functions to return a std::string/const char* or change the way you call them:
to string:
const char* isWeak() {
return " Weak";
}
// then you can do
cout << "Human is " << human.isWeak() << endl;
Or change the way you call the function:
cout << "Human is ";
human.isWeak();
Your isWeak and isStrong functions are void they do not return anything; calling cout << human.isWeak() is expecting isWeak to return something (an int, string, double, etc.).

C++ - Overloaded Operator in Derived Class not working

Okay, so the overloaded operator for the derived class is not working. It is only using the overloaded operator in the base class. Any ideas why?
Base class operator in class definition header file:
friend ostream & operator << (ostream & out, const PocketMonster & p);
Base class operator:
ostream & operator << (ostream & out, const PocketMonster & p)
{
out << endl << "(Monster Types: Type 1 = Fire, Type 2 = Water, Type 3 = Grass)" << endl
<< "PocketMonster Information: " << endl << "Name: " << p.name << endl
<< "Status (0=Dead, 1=Alive): " << p.status << endl << "Level: " << p.level << endl
<< "Strength: " << p.strength << endl
<< endl << "(Weapon Types: 1 = Fire, 2 = Water, 3 = Grass, 4 = Normal)" << endl
<< p.name << "'s Weapon Information: " << endl << "Weapon type: " << p.get_weaptype() << endl
<< "Weapon durability: " << p.get_weapdura() << endl << "Weapon level required: " << p.get_weaplvl() << endl << endl;
return out;
}
Derived class overloaded operator in class definition header file:
friend ostream & operator << (ostream & out, const FireMonster & p);
Derived class overloaded operator:
ostream & operator << (ostream & out, const FireMonster & p)
{
return out << static_cast<const PocketMonster&>(p) << endl << "FireMonster Attributes:" << endl << "Temperature: " << p.temperature << endl;
}
And here's a function where it tries to output the information
void displayLosers(vector<PocketMonster *> p)
{
for (int i=0; i<p.size(); i++)
{
if (p[i]->get_status() == false)
{
cout << p[i]->get_name() << " is a loser." << endl;
cout << *(p[i]);
}
}
}
Thanks for help in advance!
Add virtual function Output to the base class (at public or protected section):
virtual ostream & Output (ostream & out) const;
// ...
ostream & PocketMonster::Output (ostream & out) const
{
out << endl << "(Monster Types: Type 1 = Fire, Type 2 = Water, Type 3 = Grass)" << endl
<< "PocketMonster Information: " << endl << "Name: " << p.name << endl
<< "Status (0=Dead, 1=Alive): " << p.status << endl << "Level: " << p.level << endl
<< "Strength: " << p.strength << endl
<< endl << "(Weapon Types: 1 = Fire, 2 = Water, 3 = Grass, 4 = Normal)" << endl
<< p.name << "'s Weapon Information: " << endl << "Weapon type: " << p.get_weaptype() << endl
<< "Weapon durability: " << p.get_weapdura() << endl << "Weapon level required: " << p.get_weaplvl() << endl << endl;
return out;
}
and override it in derived class:
virtual ostream & Output (ostream & out) const;
// ...
ostream & FireMonster::Output (ostream & out) const
{
return out << PocketMonster::Output(out) << endl << "FireMonster Attributes:" << endl << "Temperature: " << p.temperature << endl;
}
Then rewrite operator<< for the base class in the following way:
ostream & operator << (ostream & out, const PocketMonster & p)
{
return p.Output(out);
}
and remove operator<< for derived class.