std::set

[Austin]

Here is my program:

class Test {
private:
int _num;
};

int main()
{
set<TestaSet;
Test aTest;
aSet.insert(aTe st);
return 0;
}

when compiling, vs2003 complain about operator <. If I create a class which
will be used in set, I have to implement or overload operator <? Thanks in
advance.

[Tor Einar =?UTF-8?B?VMO4bm5lc3Nlbg==?=]

Austin wrote:

Here is my program:

class Test {
private:
int _num;
};

int main()
{
set<TestaSet;
Test aTest;
aSet.insert(aTe st);
return 0;
}

when compiling, vs2003 complain about operator <. If I create a class
which
will be used in set, I have to implement or overload operator <? Thanks
in advance.

Why use Set in the first place ?

[=?ISO-8859-1?Q?Erik_Wikstr=F6m?=]

On 2007-04-29 16:28, Austin wrote:

Here is my program:

class Test {
private:
int _num;

Try not to use names which start with _, in certain scopes they are
reserved.

};

int main()
{
set<TestaSet;
Test aTest;
aSet.insert(aTe st);
return 0;
}

when compiling, vs2003 complain about operator <. If I create a class which
will be used in set, I have to implement or overload operator <? Thanks in
advance.

No you can specify another comparator to use instead, something like
this (untested):

class Test {
int num_

friend bool cmp(const Test&, const Test&);
};
bool cmp(const Test& a, const Test& b)
return a.num_ < b.num_
}

int main()
{
std::set<Test, cmps;
}

But it's usually much easier to just implement operator<.

--
Erik Wikström

[osmium]

"Austin" wrote:

Here is my program:

class Test {
private:
int _num;
};

int main()
{
set<TestaSet;
Test aTest;
aSet.insert(aTe st);
return 0;
}

when compiling, vs2003 complain about operator <. If I create a class
which
will be used in set, I have to implement or overload operator <? Thanks
in
advance.

If the set consists of fundamental types, such as int, I would expect there
would be no glitch. But you have hidden your int in a class and the
compiler has no knowledge about the innards of that class. Except for the
fear factor, it should not be a big deal. Something like (untested)

bool operator<(const Test arg) {if(_num < arg._num) return
_num<arg._num;}

[Ron Natalie]

Austin wrote:

>
when compiling, vs2003 complain about operator <. If I create a class which
will be used in set, I have to implement or overload operator <? Thanks in
advance.

Yes, set needs a "less" relation to work. This means you must either
implement operator< or you must provide a function object to the set
to accomplish that (this by default is std::less which uses the objects
operator<).

[Pete Becker]

osmium wrote:

>
bool operator<(const Test arg) {if(_num < arg._num) return
_num<arg._num;}

And what does this function return if _num is not less than arg._num? <g>

For the humor-impaired, it's obviously a typo.

--

-- Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com)
Author of "The Standard C++ Library Extensions: a Tutorial and
Reference." (www.petebecker.com/tr1book)