Please check my C++

**anon** · 07-18-2008

Well, the standard says:

13.5.3 Assignment
An assignment operator shall be implemented by a non-static member function with exactly one parameter.

It is possible to add a contructor to make Y assignable to X (in which case the constructor would do the hard work).

Code:

struct Y {};

struct X
{
    X() {}
    X(const Y&) {}
};

int main()
{
    X x;
    Y y;
    x = y;
}

**Elysia** · 07-18-2008

It should be equally possible to create an assignment operator in X that takes Y as argument.
It just can't be global.

**csonx_p** · 07-21-2008

Hello, read your posts...

But anyway, it seems that you can't overload operator= for enum types anyway since it can only be overloaded as non-static member function.

Operator = must be a member of the class to which it is defined to work with.
As thus, operator = does not work for enums, only classes.
Either way, you should not assign an int to an enum; you're essentially circumventing the whole C++ type safety.

You can certainly make "global" operator=() operator, that takes two arbitrary classes [that you have some idea of how you would convert to the left-hand side type].

The reason, I believe, for this operator is the need to serialize the data to file. If it was stored from the enum on the file, then it should be safe to read back. We could add checks in the operator to ensure that's the case.

Am not sure if i have a solution to my problem....

**Elysia** · 07-21-2008

I would say you have to cast the enum to int.
But what's the code that uses the enum that relies on that assignment operator?

**csonx_p** · 07-21-2008

Originally Posted by Elysia

I would say you have to cast the enum to int.
But what's the code that uses the enum that relies on that assignment operator?

i figured there's not even a need to assign the int, cause i have the enums to assign anyway... No need for overloading. Thanx

Car::TankStatus ts;

// Ensure correct tank details
if ( (ts>3) || (ts<0) ) {
ts=Car::unknown;
}

**csonx_p** · 07-21-2008

My sort function works but not according to my desires. I have two fields that it needs to consider when sorting [car make & car model]... i.e If i have Mercedes Vito before Mercedes Benz in the list, then the two wont be sorted since both have the same make...

this is how i use the sort function...

Code:

vector <Car> vehicle;
sort(vehicle.begin(), vehicle.end());

How do i modify this to achieve my desires?

**matsp** · 07-21-2008

You need a operator> (or is it operator<) implemented for your Car class. You would also, most likely, want to combine the effect of make and model, so for exampel Ford Escort is before Ford Focus. This would mean comparing the make first, and if they are equal, then compare the make component.

--
Mats

**csonx_p** · 07-21-2008

Originally Posted by matsp

You need a operator> (or is it operator<) implemented for your Car class. You would also, most likely, want to combine the effect of make and model, so for exampel Ford Escort is before Ford Focus. This would mean comparing the make first, and if they are equal, then compare the make component.

--
Mats

Cool, i already have that operator, just need to expand on it!

Code:

bool Car::operator<(const Car& car) const
{
	return make < car.make;
}

thnx... Sorry, how do you clear unwanted characters on stin again? is it cin.clear()?

**matsp** · 07-21-2008

Originally Posted by csonx_p

Cool, i already have that operator, just need to expand on it!

Code:

bool Car::operator<(const Car& car) const
{
	return make < car.make;
}

thnx... Sorry, how do you clear unwanted characters on stin again? is it cin.clear()?

cin.ignore() perhaps? cin.clear() sets (or rather clears) the error flags, but doesn't affect input itself. So cin.clear() may be useful if you reach EOF in a file and then want to read it again.

--
Mats

**Elysia** · 07-21-2008

Originally Posted by csonx_p

thnx... Sorry, how do you clear unwanted characters on stin again? is it cin.clear()?

http://cboard.cprogramming.com/showp...0&postcount=46

**csonx_p** · 07-21-2008

Originally Posted by Elysia

http://cboard.cprogramming.com/showp...0&postcount=46

Oh! that boost thing again... Lol! well i said am gonna return to you to explain it more, but didn't as yet... Let me try't then will flood you with questions

**csonx_p** · 07-21-2008

Code:

boost::integer_traits<int>::const_max

Please explain, what does this have to do with STDIN, what's boost anyway?

**matsp** · 07-21-2008

Originally Posted by csonx_p

Code:

boost::integer_traits<int>::const_max

Please explain, what does this have to do with STDIN, what's boost anyway?

It is simply a constant describing the largest positive value that an int can have, and nothing else. So it's really not necessary to use boost for this purpose - it's just a convenient place to get such a constant. It is also unlikely that you really need to ignore 2GB of input - most likely any number between 100 and 10000 would be perfectly find for NEARLY all purposes.

--
Mats

**csonx_p** · 07-21-2008

Thanx mats for explaining boost..

Code:

bool Car::operator<(const Car& car) const
{
	return make < car.make;
}

Q.

1. i know i wrote this but have a question... In the above, what is the different between make & car.make, is it a this pointer VS current object...?

2. I tried doing this but doesn't work...

Code:

bool Car::operator<(const Car& car) const
{
	return (make < car.make) && (model < car.model);
}

Maybe because i don't understand how does find() use the operator '<'...

**matsp** · 07-21-2008

What you need is something like this:

Code:

   return (a.x == b.x)? a.y < b.y : a.x < b.x;

Or, if we use if-statement instead of the ternary operator:

Code:

   if (a.x == b.x) return a.y < b.y;
   return a.x < b.x

--
Mats

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