Programming Forums > Application Development > C++

Arla · Nov 25th, 2007, 1:19 PM

Quote:

Originally Posted by peaceofpi

Well, I understand what you mean, but you can't return a class instance as a function result.

Really? I'd be REALLY REALLY surprised, if you can't return a struct or a class from a function. If you can't that would seem to be horribly limiting.

peaceofpi · Nov 25th, 2007, 3:30 PM

Perhaps I worded it wrong. I was incorrect when I said classes couldn't (both can be return types) but structs can't be used with << due to lack of overloading. In your original post you said structures so I took it literally.

edit: It appears I'm wrong again, apparently in C++ you can treat structs exactly like classes. Sorry for the trouble I'm causing!

DaWei · Nov 25th, 2007, 4:08 PM

The difference between a struct and a class is default access. This is one of several differences between C and C++ that people forget about when they say C++ is merely a superset of C.

peaceofpi · Nov 25th, 2007, 4:50 PM

I still haven't touched on DaWei's suggestion (error checking), but here's the final code.

 c++ Syntax (Toggle Plain Text) 
struct dms
{
	int degrees;
	int minutes;
	int seconds;
} r;
 
std::ostream& operator<< (std::ostream& os, const dms& r)
{
	os << r.degrees << " degrees " << r.minutes << " minutes "
	<< r.seconds << " seconds";
	return os;
}
 
dms deg2dms(double deg)
{
	double n = deg;
 
	r.degrees = static_cast<int>(n);
	n -= r.degrees;
	n *= 60.0;
 
	r.minutes = static_cast<int>(n);
	n -= r.minutes;
	n *= 60.0;
 
	r.seconds = static_cast<int>(n);
	if ( (n - r.seconds) >= 0.5 )
		r.seconds += 1;
 
	return r;
}
struct dms
{
	int degrees;
	int minutes;
	int seconds;
} r;

std::ostream& operator<< (std::ostream& os, const dms& r)
{
	os << r.degrees << " degrees " << r.minutes << " minutes "
	<< r.seconds << " seconds";
	return os;
}

dms deg2dms(double deg)
{
	double n = deg;

	r.degrees = static_cast<int>(n);
	n -= r.degrees;
	n *= 60.0;

	r.minutes = static_cast<int>(n);
	n -= r.minutes;
	n *= 60.0;

	r.seconds = static_cast<int>(n);
	if ( (n - r.seconds) >= 0.5 )
		r.seconds += 1;
	
	return r;
}

DaWei · Nov 25th, 2007, 6:26 PM

Why won't you investigate error checking? You might be perfect, but your users are most assuredly not. Are you a God that that you can command obedience to your wishes without considering stupid responses? I might be wrong, but I think not.

Jabo · Nov 25th, 2007, 9:35 PM

Quote:

Originally Posted by DaWei

The difference between a struct and a class is default access.

Another difference to keep in mind is that Classes are byref, structs are byval, when passing to functions; at least in VB, and I'm sure they act the same way in C++

DaWei · Nov 25th, 2007, 9:41 PM

And how sure are you? Regardless of how sure you are, you are mistaken.

lectricpharaoh · Nov 26th, 2007, 3:32 AM

Quote:

Originally Posted by Jabo

Another difference to keep in mind is that Classes are byref, structs are byval, when passing to functions; at least in VB, and I'm sure they act the same way in C++

Quote:

Originally Posted by DaWei

And how sure are you? Regardless of how sure you are, you are mistaken.

Dawei is correct. In some languages, like Java, C#, and VB.NET, classes are reference types. This means when you deal with one, the variable that holds it doesn't actually hold it, but instead holds a reference (read: pointer) to it. These objects also exist on the heap, not on the stack, so they persist until the garbage collector reclaims them (which will be an indeterminate time after the last reference goes out of scope). In C# and VB.NET, using a structure is a way around this, and allows you to use a simple value type and avoid the overhead of heap allocation and the garbage collector. For simple data records, a struct is arguably a better thing to use in some situations.

C++ classes, on the other hand, are like any other type in C++ in that they exist on the stack unless you explicitly allocate them on the heap (ie via the new operator, or equivalent).

peaceofpi · Nov 26th, 2007, 2:45 PM

DaWei, could you explain a little more about the error checking I should do? I'm open to suggestions, I just don't get what could go wrong (unless they passed a non-number to it).

lectricpharaoh · Nov 26th, 2007, 3:11 PM

Quote:

Originally Posted by peaceofpi

DaWei, could you explain a little more about the error checking I should do? I'm open to suggestions, I just don't get what could go wrong (unless they passed a non-number to it).

Well, a parameter of the wrong type would be caught by the compiler, so no worries there.

However, how do you handle conditions such as negative or greater than 360? If you're talking about motion, such as turning, then such conditions are to be expected, and should raise no concerns (though you need to decide which direction a negative measure represents). If you're talking about measurements of angles, such as the corner of a shape, then you're not going to have negatives or angles greater than 360; such parameters should be treated as errors.

Nov 25th, 2007, 3:30 PM	#12
peaceofpi hi: for(;;) goto hi; Join Date: Jun 2006 Posts: 115 Rep Power: 3	Re: Is there a better way to do this? Perhaps I worded it wrong. I was incorrect when I said classes couldn't (both can be return types) but structs can't be used with `<<` due to lack of overloading. In your original post you said structures so I took it literally. edit: It appears I'm wrong again, apparently in C++ you can treat structs exactly like classes. Sorry for the trouble I'm causing! __________________ How do you play Religious Roulette? Stand around in a circle and blaspheme till someone gets struck by lightning. Last edited by peaceofpi; Nov 25th, 2007 at 3:46 PM.

Nov 25th, 2007, 4:08 PM	#13
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Re: Is there a better way to do this? The difference between a struct and a class is default access. This is one of several differences between C and C++ that people forget about when they say C++ is merely a superset of C. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Nov 25th, 2007, 4:50 PM	#14
peaceofpi hi: for(;;) goto hi; Join Date: Jun 2006 Posts: 115 Rep Power: 3	Re: Is there a better way to do this? I still haven't touched on DaWei's suggestion (error checking), but here's the final code. c++ Syntax (Toggle Plain Text) struct dms { int degrees; int minutes; int seconds; } r; std::ostream& operator<< (std::ostream& os, const dms& r) { os << r.degrees << " degrees " << r.minutes << " minutes " << r.seconds << " seconds"; return os; } dms deg2dms(double deg) { double n = deg; r.degrees = static_cast<int>(n); n -= r.degrees; n = 60.0; r.minutes = static_cast<int>(n); n -= r.minutes; n = 60.0; r.seconds = static_cast<int>(n); if ( (n - r.seconds) >= 0.5 ) r.seconds += 1; return r; } struct dms { int degrees; int minutes; int seconds; } r; std::ostream& operator<< (std::ostream& os, const dms& r) { os << r.degrees << " degrees " << r.minutes << " minutes " << r.seconds << " seconds"; return os; } dms deg2dms(double deg) { double n = deg; r.degrees = static_cast<int>(n); n -= r.degrees; n = 60.0; r.minutes = static_cast<int>(n); n -= r.minutes; n = 60.0; r.seconds = static_cast<int>(n); if ( (n - r.seconds) >= 0.5 ) r.seconds += 1; return r; } __________________ How do you play Religious Roulette? Stand around in a circle and blaspheme till someone gets struck by lightning.

Nov 25th, 2007, 6:26 PM	#15
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Re: Is there a better way to do this? Why won't you investigate error checking? You might be perfect, but your users are most assuredly not. Are you a God that that you can command obedience to your wishes without considering stupid responses? I might be wrong, but I think not. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Nov 25th, 2007, 9:41 PM	#17
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Re: Is there a better way to do this? And how sure are you? Regardless of how sure you are, you are mistaken. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Nov 26th, 2007, 2:45 PM	#19
peaceofpi hi: for(;;) goto hi; Join Date: Jun 2006 Posts: 115 Rep Power: 3	Re: Is there a better way to do this? DaWei, could you explain a little more about the error checking I should do? I'm open to suggestions, I just don't get what could go wrong (unless they passed a non-number to it). __________________ How do you play Religious Roulette? Stand around in a circle and blaspheme till someone gets struck by lightning.

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Programming Forums > Application Development > C++

Is there a better way to do this?