Re: Best way to organize my sorting funtcors?

From:

Steve555 <foursheds@btinternet.com>

Newsgroups:

comp.lang.c++

Date:

Sun, 7 Dec 2008 05:48:58 -0800 (PST)

Message-ID:

<767fd363-36f7-49b3-8401-3cecda3fe3d7@j35g2000yqh.googlegroups.com>

On 7 Dec, 13:32, zr <zvir...@gmail.com> wrote:

On Dec 7, 3:07 pm, Steve555 <foursh...@btinternet.com> wrote:

On 7 Dec, 12:45, zr <zvir...@gmail.com> wrote:

On Dec 7, 1:53 pm, Steve555 <foursh...@btinternet.com> wrote:

Hi,

I've ended up with many, many operator< functors like this

bool operator<(UserRating lhs, UserRating rhs) {
return lhs.userID < rhs.userID;

}

to sort the many custom structs I have, and the typedefined vectors=

have to store them.
All of the structs and their vectors are neatly organized in to one
myVecDefiness.h file, but the functors are dotted about all over th=

place. If I try to put them in myVecDefiness.h (or any other header=

then the compiler complains of multiple definitions (even though I
have #ifndef etc. in the header). But if I put them in a single .cp=

then the compiler doesn't find them.

What's the neatest way to organize this?

Thanks

Steve

Just a thought.
If all of your classes contain an ID field, you could consider
inheriting them all from a common base class that contains that field=

That way you will only need to define one comparison operator for the
base class.

class BaseClass
{
friend bool operator<(const BaseClass& a, const BaseC=

lass& b);

//...
protected:
int id;

};

bool operator<(const BaseClass& a, const BaseClass& b)
{
return a.id < b.id;

}

class A : public BaseClass
{
//...

};

class B : public BaseClass
{
//...

};

Beware: this will allow comparisons between objects of different type=

if their classes inherit from BaseClass:
A a;
B b;
a < b; //ok

Thanks for the idea, that would clean things up a lot, but I'm not
sure if I can afford the over head of converting mu structs to classes
as I'm trying to fit millions in to limited memory. Any idea what the
cost of this would be on a typical struct that might contain two
shorts, one long, and a float?

See these topics:http://www.parashift.com/c++-faq-lite/classes-and-object=

s.html#faq-7.8http://www.parashift.com/c++-faq-lite/virtual-functions.html#=
faq-20.4

Bottom line: if you do not define any virtual method in your class,
the overhead is zero.

Yup, to quote from the first link:
"A class feels like a living and responsible member of society with
intelligent services, a strong encapsulation barrier, and a well
defined interface."
Exactly my mental block. I'm glad we got on this topic because I think
I'll be less hesitant about using classes in future.