How to Overload the Operator++ in Two Different Ways for Postfix A++ and Prefix ++A

How to overload the operator++ in two different ways for postfix a++ and prefix ++a?

Should look like this:

class Number 
{
    public:
        Number& operator++ ()     // prefix ++
        {
           // Do work on this.   (increment your object here)
           return *this;
        }

        // You want to make the ++ operator work like the standard operators
        // The simple way to do this is to implement postfix in terms of prefix.
        //
        Number  operator++ (int)  // postfix ++
        {
           Number result(*this);   // make a copy for result
           ++(*this);              // Now use the prefix version to do the work
           return result;          // return the copy (the old) value.
        }
}; 

how to apply operator overloading for unary postfix operator

if you want post-inc/dec then the code will be :

  Distance operator++ (int) {
     feet = feet+1;
     inches = inches+1;
     
     return Distance(feet, inches);
  }

we use int in formal parameter . it is just crate different between post/pre-fix.
The prefix form of the operator is declared exactly the same way as any other unary operator; the postfix form accepts an extra argument of type int.

overloading postfix and prefix operators

The pre- and post-increment are two distinct operators, and require separate overloads.

C++ doesn't allow overloading solely on return type, so having different return types as in your example wouldn't be sufficient to disambiguate the two methods.

The dummy argument is the mechanism that the designer of C++ chose for the disambiguation.

Overloading operator++ prefix / postfix in terms of each other?

Boost provides this functionality in the Boost Operators utility library. Its implementation is a little different, but achieves the same result.

Can I / Should I use this trick?

Use it wherever you can; cutting out redundant and repetitive code is a fundamental principle of refactoring and is a good practice to get into.

Have I just reinvented the wheel again, or have I just created a useful small library that could be aggregated to such kinds of projects?

I guess you could say then that you've reinvented the wheel. I don't think that's necessarily a bad thing, though: I find that if I implement something myself I usually understand it much better and learn a lot through the process.

Prefix and Postfix operator overloading in C#

You're trying to adjust a type that is declared as class to behave as a struct. This doesn't make any sense for me. If you change class Test to struct Test, remove the parameterless constructor and override the .ToString method, all the problems are gone.

First, You're creating a new instance of Test each time you increment (Post or Pre). So when you hit this line:

Test obj2 = ++obj;

As if you're writing:

obj = new Test(obj.x + 1);
Test obj2 = obj;

Second and as for the printing issue, just override the ToString:

public override string ToString()
{
    return x.ToString();
}

c++ postfix / prefix operator overload as non-member function

Perhaps I misunderstood, but if you're struggling with proper declaration of both operators, you can still do this with free operators like members. You do, however, need to pass the object as the first parameter by-reference. You're correct that as member functions they get their object for free via this. As a free function, you need to push it yourself.

#include <iostream>

struct my_array
{
    // your members here.
};

my_array& operator ++(my_array& obj)
{
    // access to members is through obj.member
    std::cout << "++obj called." << std::endl;
    return obj;
}

my_array operator ++(my_array& obj, int)
{
    my_array prev = obj;

    // modify obj, but return the previous state.        
    std::cout << "obj++ called." << std::endl;

    return prev;
}

int main(int argc, char *argv[])
{
    my_array obj;
    ++obj;
    obj++;
    return 0;
}

Output

++obj called.
obj++ called.

C++ postfix ++ operator overloading

The caller now has to deal with deleting the memory.

C# postfix and prefix increment/decrement overloading difference

This is the wrong way to implement increment and decrement in C#. You will get crazy results if you do it wrong; you did it wrong, you got crazy results, so the system works. :-)

Coincidentally I wrote an article about this very subject last week:

http://ericlippert.com/2013/09/25/bug-guys-meets-math-from-scratch/

As commenter dtb points out, the correct implementation is:

    public static Counter operator ++(Counter c)
    {
        return new Counter(c.v + 1);
    }

In C# the increment operator must not mutate its argument. Rather it must only compute the incremented value and return it, without producing any side effects. The side effect of mutating the variable will be handled by the compiler.

With this correct implementation your program now goes like this:

    Counter c1 = new Counter(1);

Call the object that c1 refers to right now W. W.v is 1.

    Counter c2 = c1++;

This has the semantics of:

temp = c1
c1 = operator++(c1) // create object X, set X.v to 2
c2 = temp

So c1 now refers to X, and c2 refers to W. W.v is 1 and X.v is 2.

    Counter c3 = ++c1;

This has the semantics of

temp = operator++(c1) // Create object Y, set Y.v to 3
c1 = temp
c3 = temp

So c1 and c3 now both refer to object Y, and Y.v is 3.

    c3++;

This has the semantics of

c3 = operator++(c3) // Create object Z, set Z.v to 4

So when the smoke all clears:

c1.v = 3 (Y)
c2.v = 1 (W)
c3.v = 4 (Z)

and X is orphaned.

This should give exactly the same results as if you'd had c1, c2 and c3 as normal integers.

---

Related Topics