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Alisdair Meredith (TeamB)
Guest
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 Posted: Fri Oct 08, 2004 4:29 pm Post subject: Re: find_if error searching for struct with matching member |
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Leo Siefert wrote:
| Quote: | struct TMatch {
AnsiString Data;
TTreeNode* Node;
bool equalsNode( TTreeNode* );
};
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This function works with pointers.
| Quote: | class TForm1 : public TForm
{
__published:
private:
std::vector<TMatch> Matches;
std::vector<TMatch>::iterator TMatchIterator;
public:
__fastcall TForm1( TComponent* Owner );
};
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The vector stores objects-by-value.
Functor should be passing objects by reference-to-const.
| Quote: | __fastcall TForm1::TForm1( TComponent* Owner ) : TForm( Owner )
{
TTreeNode *node;
TMatchIterator it =
std::find_if (
Matches.begin(),
Matches.end(),
std::bind2nd(
std::mem_fun_ref( &TMatch::equalsNode ),
node
)
); // ERROR
}
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I strongly recommend taking a look at the boost::bind library, soon to
be part of the standard library Technical Report. It is *much* simpler
than bind1st/2nd. mem_fun_ref and all that. Everything is handled by
the single bind template.
std::find_if (
Matches.begin(),
Matches.end(),
boost::bind( &TMatch::equalsNode, node, _1 )
)
);
AlisdairM(TeamB)
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Gillmer J. Derge [TeamB]
Guest
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| Posted: Fri Oct 08, 2004 4:35 pm Post subject: Re: find_if error searching for struct with matching member |
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Leo Siefert wrote:
| Quote: | I would appreciate any help, including a better basic approach. (Can I
do this with just function adapters and avoid functions dedicated to
searching for specific fields?)
|
I think find_if is definitely the right basic approach. This is exactly
what it's for. I think you could do it with just function adapters
(adapting a getter and composing it with equals and bind2nd) if you use
some of the boost classes but not with plain old standard library C++.
As for the error, I haven't actually compiled this, but the following
things strike me looking at it.
| Quote: | bool equalsNode( TTreeNode* );
|
Should probably be:
bool equalsNode(const TTreeNode*) const;
| Quote: | std::vector<TMatch>::iterator TMatchIterator;
[...]
TMatchIterator it =
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Is TMatchIterator supposed to be a type or a member? You've declared it
as a member of the class but you're using it here like it's a type. I
suspect that's the cause of the error. The compiler is as confused as I
am. :-)
--
Gillmer J. Derge [TeamB]
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Gillmer J. Derge [TeamB]
Guest
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| Posted: Fri Oct 08, 2004 7:37 pm Post subject: Re: find_if error searching for struct with matching member |
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Leo Siefert wrote:
| Quote: | What I would really like to find is a way to avoid needing to have a
dedicated function for searching on each field of the data structure.
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Assuming that a getter doesn't count as a dedicated function, I think
something like this would work (untested, and I've never really used
boost::bind, but this looks like more or less the right idea) ...
bind(std::equals<TTreeNode*>(), node,
bind(mem_fun_ref(&TMatch::getNode), _1))
I think this should turn into something equivalent to:
std::equals<T>(node, x.getNode());
--
Gillmer J. Derge [TeamB]
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Chris Uzdavinis (TeamB)
Guest
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| Posted: Fri Oct 08, 2004 7:48 pm Post subject: Re: find_if error searching for struct with matching member |
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Leo Siefert <lIHATESPAMsiefert (AT) senate (DOT) michigan.gov> writes:
| Quote: | What I would really like to find is a way to avoid needing to have a
dedicated function for searching on each field of the data structure.
In this case, if I want to search for a match to the Data member it
seems that I need to add an additional functor to allow that. Not a
very scalable approach and I would like to find something better.
|
It does not have to be a member function, though. If you
decide--later--to add another sort ordering or comparison function,
you can do that in your own "user" code withotu touching the
declaration of the objects in the container.
--
Chris (TeamB);
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