Studying operator overloading

[Alex_Brazil]

I'm studying operator overloading and can not understand how that is identified using the + + operator pre-set or post-set.

------ CODE --------------------------------------------------

#include <iostream>
using namespace std;

class ponto
{

private:

int x,y;

public:

ponto(int x1=0, int y1=0) {x=x1;y=y1;} // Constructor

ponto operator ++() //Function operator PRE-FIXED
{

++x;++y;

return ponto(x,y);

}

ponto operator ++(int) //Function operator POS-FIXED
{

++x;++y;

return ponto(x-1,y-1);

}

void printpt() const
{

cout <<'('<< x <<','<<y<<')';

}

};

void main()
{

ponto p1,p2(2,3),p3;
cout << "\n p1 = "; p1.printpt();
cout << "\n p2 = "; p2.printpt();
cout << "\n++p1 = ";
(++p1).printpt(); //increases after use
cout << "\np2++ = ";
(p2++).printpt(); //uses after incrases
cout << "\n p2 = "; p2.printpt();
p3 = p1++; //assigns after increases
cout << "\n p3 = "; p3.printpt();
cout << "\n p1 = "; p1.printpt();

}

[Paul McKenzie]

I'm studying operator overloading and can not understand how that is identified using the + + operator pre-set or post-set.

First, use proper code tags when posting code. There is no need for "Indent" tags if you just posted using code tags:


[code]
Your code goes here
[/code]

Example:

#include <iostream>

int main()
{
   std::cout << "Hello World";
}

See how the code looks when I post as compared to when you post code?

Second, if you're studying operator overloading, why are you using such a confusing and wrong piece of code to study this? Please see the FAQ on overloading ++ here, and compare the simple example and explanation of this operator and how it is to be overloaded to what you're doing.

http://www.parashift.com/c++-faq/inc...erloading.html

The first glaring issue is that the prefix ++ should be returning a reference to the current object, and your code doesn't do that.

Regards,

Paul McKenzie

[Alex_Brazil]

I am grateful for the support I have received from members of this forum and apologize for the mistakes of posting, no formatting required.

I created a new code to study the overhead of a binary operator, where the operator +, but the compiler returns the following error: "main.obj: -1: error: LNK2019: unresolved external symbol" public: __ thiscall sale sale :: (void) "(? 0venda @ @ QAE @ XZ) referenced in function _main".

I do not understand what is generating the error. Can anyone help me?

Follow the code:

#include <iostream>
#include <iomanip>

using namespace std;

class venda
{
    private:
        int npecas;
        float precos;
     public:
        venda();
        venda(int np, float p) {npecas = np;precos = p;}
        venda operator + (venda v) const;
        void getvenda()
        {
            cout << "\nInsira o nr de pecas: "; cin >> npecas;
            cout << "\nInsira o preco: "; cin >> precos;
        }
        void printvenda() const;
};

//int venda::npecas;
//float venda::precos;

venda venda::operator +(venda v) const
{
    int pec = npecas + v.npecas;
    float pre = precos + v.precos;
    return venda(pec,pre);
}
void venda::printvenda() const
{
    cout << setiosflags(ios::fixed)
         << setiosflags(ios::showpoint)
         << setprecision(2)
         << setw(10) <<npecas;
    cout << setw(10) << precos << '\n';
}

void main()
{
    venda A(58,34.53), B, C(30,60.3), T, Total;
    B.getvenda();
    T = A + B;
    Total= A + B + C;

    cout << "Venda: A .............."; A.printvenda();
    cout << "Venda: B .............."; B.printvenda();
    cout << "Venda: A + B .........."; T.printvenda();
    cout << "Venda: Totais A+B+C...."; Total.printvenda();
}

[GCDEF]

This line.
venda();

You declared a constructor but didn't give it a body.

[Alex_Brazil]

Thank you. The problem was solved.

[Alex_Brazil]

Operator Overloading - object returns wrong value

Another example I created for my study, but the objects s3, s4 and s5 are returning wrong values​​. Someone knows you explain why?

#include <iostream>
#include <string>

const int MAX = 80;
using namespace std;

class string2
{
    private:
        char str[MAX];
    public:
        string2() {str[0]='\0';}
        string2(char s[]) {strcpy(str,s);}

        string2 operator +=(string2 s) const //Concatena
        {
            string2 temp;
            if(strlen(str)+strlen(s.str) < MAX)
            {
                strcpy(temp.str,str);
                strcat(temp.str,s.str);
            }
            else

                cout << "\nMemor;ia Cheia!";
    
            return temp;
         }

            string2 operator +(string2 s) const // Concatena
            {
                string2 temp;
                temp +=s.str;
                return temp;
            }

            void print() const {cout << str;}
};

int main()
{
    string2 s1("Feliz Aniversario! "),
            s2("Denise."),
            s3("Bom Dia! "), s4, s5;
    cout << "\ns1 = "; s1.print();
    cout << "\ns2 = "; s2.print();

    s3 += s2;
    s4 = s1 + s2;
    s5 = s1 + s1;

    cout << "\ns3 = "; s3.print();
    cout << "\ns4 = "; s4.print();
    cout << "\ns5 = "; s5.print();
}

[Paul McKenzie]

Operator Overloading - object returns wrong value

Another example I created for my study,

You need to study a bit more before creating your own examples:

       string2 operator +=(string2 s) const //Concatena

Why are you passing string2 objects by value? You should be passing them by const reference, not by value.

string2 operator +=(string2 s) const //Concatena

Why is operator += returning a new object? It should be returning a reference to the existing object. That is the whole purpose of +=. It takes the existing object, adds something to it, and returns the existing object.

Everything I pointed out is covered in good books. Are you learning from real books? If you're just throwing things together without any guidance, that is not the way you learn C++. You're supposed to be using good books (and tutorials) on the language, i.e. see how the experts in the language do things. Putting stuff together yourself just leads to mistakes and a misunderstanding of how to use C++ properly.

Regards,

Paul McKenzie