How to properly Use remove_if?

Question

I am attempting to use the remove_if for an array. The array contains objects of songs which contain 2 string properties (artist and title). I have a bool equals operator but have issues with implementation. Below is my Song equals operator:

bool Song::operator==(const Song& s) const 
{
    return (title_ == s.GetTitle() && artist_ == s.GetArtist()) ?  true : false;
}

I have another function which is supposed to remove the song if either title or artist match the parameters passed into it. Then returns the number of songs removed:

unsigned int Playlist::RemoveSongs(const string& title, const string& artist) 
{
    int startSize = songs_.size();
    Song s = Song(title,artist);
    // below are some of the things I've attempted from documentation
    //songs_.remove_if(std::bind2nd(std::ptr_fun(Song::operator()(s))));
    //std::remove_if(songs_.begin(),songs_.end(),s);
    int endSize = songs_.size();
    return startSize - endSize;
}

_I have another function which is supposed to remove the songs if either title or artist match_ but your `operator==` only checks if both the title AND artist match. You also haven't really asked a question: presumably there's something wrong with your code, but you haven't explained what is happening. — Tas, May 18 '18 at 21:25
if you create value, `remove` seems more appropriate than `remove_if` which expects predicate. — Jarod42, May 18 '18 at 21:25
oh thanks for the catch on that return statement. songs_ is a list. The Song class contains 2 strings properties for Artist and Title. — Potion, May 18 '18 at 21:26
As a side note `std::bind2nd` and `std::ptr_fun` are removed in the latest version of the Standard - they shouldn't be used. — DeiDei, May 18 '18 at 21:27
Related to [listremove-if-using-operator-with-stdfunction](https://stackoverflow.com/questions/50419292/>listremove-if-using-operator-with-stdfunction) — Jarod42, May 18 '18 at 21:27
@Tas good point. This is just one of many functions I have which covers AND, OR, XOR or Neither. For this question I am just using a small example. — Potion, May 18 '18 at 21:28
Are you sure the second condition is what you want? Also, please refrain from completely changing the question after getting an answer. — Deduplicator, May 18 '18 at 23:20

Pavan Chandaka · Accepted Answer · 2018-05-18T23:03:43.033

0

Try using lambda... Something like below (not tested). Do not forget to use "[=]" to capture out of scope variables.

std::remove_if(songs_.begin(), 
                   songs_.end(),
                   [=](Song &s){return (title == s.GetTitle() && artist == s.GetArtist()) ;})

edited May 18 '18 at 23:03

answered May 18 '18 at 21:32

Pavan Chandaka

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Okay this would be the correct answer. What can I do in the case of this error since my original structure does not have copy 'object of type 'Song' cannot be assigned because its copy assignment operator is implicitly deleted ' – Potion May 18 '18 at 21:52
2

Then use `(Song const& s)` for the parameter. – Eljay May 18 '18 at 22:11
Do not use const. Just say (Song &s) – Pavan Chandaka May 18 '18 at 23:00

How to properly Use remove_if?

1 Answers1