Turning remove_if into remove_not_if

Question

How can I reverse a predicate's return value, and remove the elements that return false instead of true?

Here is my code:

headerList.remove_if(FindName(name));

(please ignore lack of erase)

with FindName a simple functor:

struct FindName
{
    CString m_NameToFind;

    FindInspectionNames(const CString &nameToFind)
    {
        m_NameToFind = nameToFind;
    }

    bool operator()(const CHeader &header)
    {
        if(header.Name == m_NameToFind)
        {
            return true;
        }

        return false;
    }
};

I would like something like:

list.remove_if(FindName(name) == false);

Not yet using c++0x, so lambdas not allowed, sadly. I'm hoping there is a nicer solution than writing a NotFindName functor.

score 15 · Accepted Answer · edited Oct 20 '12 at 20:39

15

Check not1 in the <functional> header:

headerList.remove_if( std::not1( FindName( name ) ) );

Oh, and this:

if(header.Name == m_NameToFind)
{
    return true;
}

return false;

Please don't do that.

return ( header.Name == m_NameToFind );

That's much better, isn't it?

edited Oct 20 '12 at 20:39

answered Oct 05 '10 at 14:31

DevSolar

67,862
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1

Thanks, it works with the following mods: Functor needs to inherit from std::unary_function operator() needs to be a const member function – DanDan Oct 05 '10 at 14:42
1

Actually inheritance is not necessary, but you need to define the proper typedef that it gives you for free. As for the `const`-ness, it goes without saying :) – Matthieu M. Oct 05 '10 at 18:48

score 3 · Answer 2 · answered Oct 05 '10 at 15:42

alternatively you could use boost bind so you don't have to write that unary_function struct:

bool header_has_name (const CHeader& h, const CString& n) {return h.name == n;}

headerList.remove_if (boost::bind (header_has_name, _1, "name"));

and for remove_if_not:

headerList.remove_if (!boost::bind (header_has_name, _1, "name"));

You could even use std::equal() to avoid the header_has_name function completely but at that point it becomes a little bit ugly.

score 0 · Answer 3 · answered Oct 05 '10 at 14:29

0

Unfortunately I think writing a NotFindName functor is your best bet.

answered Oct 05 '10 at 14:29

Timo Geusch

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70

Turning remove_if into remove_not_if

3 Answers3