[[:improve]]

CPlusPlus oder auch (C++) ist eine objektorientierte Programmiersprache. Siehe auch [[coding:c|C]]/[[coding:csharp|C#]].

[[https://en.cppreference.com/w/cpp/keyword|Cpp reference]]

  * explicit - makes a conversion constructor to non-conversion constructor. [[https://weblogs.asp.net/kennykerr/Explicit-Constructors|A good Write up]]
  * virtual - override class method
  * mutable - when you have a const class but want to change parts of it.

=====Classes=====

Klassen mit mindestens einer "virtual" Funktion nennt man Polymorphe Klassen.


<code cpp>
#include <iostream>
#include <string>
#include <vector>

using namespace std;

class Token {
    private:
        std::string type;
        std::string value;        
    public:
        Token() { }
        Token(std::string _type, std::string _value) {
            type = _type;
            value = _value;
        }
        ~Token() { }
        std::string _value() { 
            return value; 
        }
    	std::string _type() { 
            return type; 
        }
        std::string str() {
            if(type == "STRING") return ("Token(" + type + ", \"" + value + "\")");
            else return ("Token(" + type + ", '" + value + "')");
        }        
};

class ASTNode {
    public:        
        std::vector<ASTNode*> child;                        	
        Token token;                        
        ASTNode() { }                        
    	ASTNode(Token _token) {
    		token = _token;
    	}         
        ~ASTNode() { }         
    	void make_child(ASTNode _node) {
    		ASTNode *temp = new ASTNode(_node._token());
    		temp->child = _node.child;
    		child.push_back(temp);
    	}            
    	Token _token() {
    		return token;
    	} 
        void show(int level) {                
            std::cout << std::string(level * 2, ' ') << token.str() << "\n";   
            for(auto it = child.begin(); it != child.end(); it++) (*it)->show(level + 1);
    	}                     
};

int main () { 

   ASTNode ast = ASTNode(Token("STMT_LIST", "STMT_LIST"));
   
   ASTNode ass = ASTNode(Token("ASSIGN", "="));
   ass.make_child(Token("VARIABLE", "f"));
   ass.make_child(Token("FLOAT", "3.14159"));   
   ast.make_child(ass);
   
   ass = ASTNode(Token("ASSIGN", "="));
   ass.make_child(Token("VARIABLE", "g"));
   ass.make_child(Token("FLOAT", "1.05"));   
   ast.make_child(ass);
   
   ASTNode reass = ASTNode(Token("ASSIGN", "="));
   reass.make_child(Token("VARIABLE", "fg"));   
   ASTNode readd = ASTNode(Token("ADD", "+"));   
   readd.make_child(Token("VARIABLE", "f"));
   readd.make_child(Token("VARIABLE", "g"));   
   reass.make_child(readd);
   
   ast.make_child(reass);

   ast.show(0);
   
   return 0;
}
</code>

See also [[coding:c#classes|classes in c]]
=====Local Classes=====

<code cpp>
void bar()
{
   struct LocalClass
   {
       int operator()(int a, int b) const { return a + b; }
   } f;

   int n = f(1, 2);
}
</code>

=====Local Structs=====

Pre C++11, ''localize'' a function to a function

<code cpp>
int foo () {
    struct Local {
        static int bar () {
            return 1;
        }
    };
    return Local::bar();
}
</code>

<code cpp>
int foo (int x) {
    struct Local {
        int & x;
        Local (int & x) : x(x) {}
        int bar (int y) {
            return x * x + y;
        }
    };
    return Local(x).bar(44);
}
</code>

=====Functor=====

A functor is pretty much just a class which defines the operator(). That lets you create objects which "look like" a function:

<code cpp>
#include <iostream>

struct add_x {
    add_x(int val) : x(val) {}  // Constructor
    int operator()(int y) const { return x + y; }
 
    private:
        int x;
};

int main() {
 
    add_x add42(42); 
    int i = add42(8); 
    printf("%d", i);
    
    return 0;
 
}
</code>

=====Templates=====

Templates werden mit dem Schlüsselwort "template" eingeleitet, gefolgt von der Template-Deklaration in spitzen Klammern ("<" und ">"). In der Template-Deklaration werden die Template-Parameter definiert, die den generischen Datentyp repräsentieren.

<code cpp>
#include <iostream>

template <typename T>
void swap(T& a, T& b) {
    T temp = a;
    a = b;
    b = temp;
}

template <typename T>
class Stack {
private:
    T* data;
    int size;
    int capacity;
public:
    Stack(int capacity) {
        this->capacity = capacity;
        this->size = 0;
        this->data = new T[capacity];
    }

    void push(const T& element) {
        if (size < capacity) {
            data[size] = element;
            size++;
        } else {
            std::cout << "Stack is full. Cannot push element." << std::endl;
        }
    }

    T pop() {
        if (size > 0) {
            size--;
            return data[size];
        } else {
            std::cout << "Stack is empty. Cannot pop element." << std::endl;
            return T(); // Return a default value for type T
        }
    }
};

int main() {
    int a = 5, b = 10;
    swap(a, b);  // Der Compiler generiert swap<int>(a, b)

    double x = 2.5, y = 7.8;
    swap(x, y);  // Der Compiler generiert swap<double>(x, y)

    Stack<int> intStack(10);
    intStack.push(1);
    intStack.push(2);
    intStack.push(3);
    int poppedIntElement = intStack.pop();
    std::cout << "Popped element: " << poppedIntElement << std::endl;
    
    Stack<double> doubleStack(10);
    doubleStack.push(1.2);
    doubleStack.push(2.4);
    doubleStack.push(3.14159);
    double poppedDoubleElement = doubleStack.pop();
    std::cout << "Popped element: " << poppedDoubleElement << std::endl;

    return 0;
}
</code>

  * [[http://www.cplusplus.com/doc/oldtutorial/templates/]]
  * [[https://www.codeproject.com/Articles/48575/How-to-define-a-template-class-in-a-h-file-and-imp|Codeproject article]]
  * http://www.willemer.de/informatik/cpp/cpptempl.htm
  * http://www.angelikalanger.com/Articles/Cuj/ExpressionTemplates/ExpressionTemplates.htm

<code cpp>
#include <iostream>

using namespace std;
template <typename T1, typename T2> void display(T1 x, T2 y);

int main(){
	display(1,2);
	display("Hello",3.14159);
	return 0;
}

template <typename T1, typename T2> void display(T1 x, T2 y) {
	std::cout << x << " and "  << y << "\n";
}
</code>

<code cpp>
#include <iostream>

using namespace std;

template <class TYPE>
class Calculator{
    public:
        Calculator();
        TYPE Add(TYPE param1, TYPE param2);
};

template <class TYPE>
Calculator<TYPE>::Calculator() {}

template <class TYPE>
TYPE Calculator<TYPE>::Add(TYPE param1, TYPE param2) {
    cout << "Calculator::sum " << param1 << " " << param2 << endl;
    TYPE result = param1 + param2 ;
    return result;
}

int main(int argc, const char * argv[]) {

    Calculator<int> calcI;
    cout << "outI : " << calcI.Add(65, 66) << "\n";
    
    Calculator<float> calcF;
    cout << "outF : " << calcF.Add(6.5, 6.6) << "\n";

    Calculator<string> calcS;
    cout << "outS : " << calcS.Add("A", "B") << "\n";

    return 0;
    
}
</code>

You can fake templates in c using [[coding:c#preprocessing|preprocessing]]

=====Closures=====

<code cpp>
void foo()
{
   auto f = [](int a, int b) -> int { return a + b; };

   auto n = f(1, 2);
}
</code>

=====Polymorphism=====

Use keyword virtual to override class methods. [[https://www.youtube.com/watch?v=kxKKHKSMGIg|Youtube - c++ Polimorphism]]

<code cpp>
#include <iostream> 
using namespace std;
 
class Shape {
    protected:
        int width, height;
      
    public:
        Shape( int a = 0, int b = 0){
            width = a;
            height = b;
        }
        virtual int area() {
            cout << "Shape area: ";
            return 0;
        }
};
class Rectangle: public Shape {
    public:
        Rectangle( int a = 0, int b = 0):Shape(a, b) { }
    
        int area () { 
            cout << "Rectangle area: ";
            return (width * height); 
        }
};

class Triangle: public Shape {
    public:
        Triangle( int a = 0, int b = 0):Shape(a, b) { }
      
        int area () { 
            cout << "Triangle area: ";
            return (width * height / 2); 
        }
};

int main() {
    Shape *shape;
    Rectangle rec(13,5);
    Triangle tri(5,13);
    shape = &rec;
    std::cout << shape->area() << endl;
    shape = &tri;
    std::cout << shape->area() << endl;
    return 0;
}
</code>

=====Singletons=====

<code cpp>
#include <iostream>
using namespace std;

class Singleton {

    public:
        static Singleton* getInstance() {
            if (m_instance == NULL)       
                m_instance = new Singleton;
            return m_instance;
        }
    
    private:
        // private constructor and destructor
        Singleton() { cout << "Instance created!\n"; }
        ~Singleton() {}
        // private copy constructor and assignment operator
        Singleton(const Singleton&);
        Singleton& operator=(const Singleton&);
        static Singleton *m_instance;
        
};

Singleton* Singleton::m_instance = nullptr;

int main(int argc, const char * argv[]) {

    Singleton *singleton;
    singleton = singleton->getInstance();
    cout << singleton << "\n";

    Singleton *anotherSingleton;
    anotherSingleton = anotherSingleton->getInstance();
    cout << anotherSingleton << "\n";

    return 0;
}
</code>

=====Constants=====

Das Schlüsselwort "const" (konstant) wird verwendet um zu definieren dass eine Variable oder ein Objekt nicht verändert werden kann. Ein Versuch den Wert zu ändern, führt zu einem Kompilierungsfehler. 

<code cpp>
const int x = 5;
x = 10;  // Kompilierungsfehler: Assignment an eine konstante Variable nicht erlaubt
</code>

Mit einer Konstanten kann man z.B auch die Länge eines Array zur Laufzeit definieren.

<code cpp>
const int arraySize = 10;
int myArray[arraySize];  // Verwendung eines konstanten Ausdrucks für die Arraygröße
</code>

See also [[coding:c#constants|constants in C]]

=====Punning=====

"Type punning" bezieht sich auf die Praxis, Speicherbereiche mit einer bestimmten Datentyp-Interpretation zu verwenden, die nicht dem ursprünglichen Typ entsprechen, um auf die darin enthaltenen Daten zuzugreifen. Ein klassisches Beispiel ist die Manipulation von Bits innerhalb eines Integers, um spezielle Flags oder Optionen zu setzen oder zu überprüfen.

<code cpp>
unsigned int options = 0;
options |= (1 << 2); // Set the third bit to 1
options &= ~(1 << 0); // Clear the first bit
</code>

  * Pointer conversion
  * union
  * reinterpret_cast

Type punning wird nicht als "good practice" angesehen weil Datentypen auf verschiedene Weisen von Systemen interpretiert werden können..

=====Casting=====


=====Links=====

[[https://www.heise.de/developer/artikel/C-20-Die-vier-grossen-Neuerungen-4568956.html|C++ 20 Neuerungen]]