Help implementing std::remove_if?

[wh1t3crayon]

I'm trying to iterate through a vector and delete elements in it. I've seen that std::remove_if is probably the best way to go about doing this, but I need help with the Predicate argument of the function. Here is my code + explanation:

void Level::RemoveLine(int line){
	std::cout << "removing line " + line;
	levelRects_.erase(std::remove_if(levelRects_.begin(), levelRects_.end(), TestForLine(line) == true), levelRects_.end());
}

bool Level::TestForLine(int line){
	for(int i = 0; i < gamePieces_.size(); i++){
		//test for each brick's line being equal to line, return true
		for(int j = 0; j < 4; j++){
			if(gamePieces_[i].GetPieceRectangles()[j].GetActiveLine() == line){
				return true;
			}
			else{
				return false;
			}
		}
	}
}

TestForLine() is supposed to be the predicate for std::remove_if, but I don't know exactly how to use it as a predicate. This code throws a compiler error "C2064 term does not evaulate a function taking one arguments". So I want to erase objects from a vector if their function TestForLine() returns true; how do I put that into terms for std::remove_if?

[MiiNiPaa]

It looks like you won't be able to use remove_if here.

Predicate is a function/functor which takes one argument arnd returns true of false depending on it.
Unless your levelRects_ contains int, you cannot use TestForLine as predicate.

And due to how it is written, you can simplify your TestForLine:

bool Level::TestForLine(int line){
    return gamePieces_[0].GetPieceRectangles()[0].GetActiveLine() == line
}

[coder777]

The thid parameter is a function (like). See:

http://www.cplusplus.com/reference/algorithm/remove_if/?kw=remove_if

[wh1t3crayon]

levelRects_ contains class objects. So if I can't use std::remove_if, what can I use to erase elements from the vector?

[MiiNiPaa]

what can I use to erase elements from the vector?

You can use a remove_if. You jkust need a funtion which takes a reference to object and decided if it needs to be removed. TestForLine is not suits this for obvious reasons (actually it kinda pointless)

[coder777]

You may use lambda:

http://www.cprogramming.com/c++11/c++11-lambda-closures.html

like so:

levelRects_.erase(std::remove_if(levelRects_.begin(), levelRects_.end(), 
[&] (const levelRect& lr) { return lr.GetLine() == line; }
), levelRects_.end());

[wh1t3crayon]

So I need a function (let's keep the name TestForLine) that takes a reference to the class object inside the vector, like so?
bool Level::TestForLine(Brick &brick)
Also, my problem is that I need to pass line down to TestForLine(). The compiler won't let me include line as a parameter but how else can the Brick objects check if their line is equal to the line parameter?

@coder777 that seems like it would work, but lr.GetLine() throws this error:

	5	IntelliSense: the object has type qualifiers that are not compatible with the member function
            object type is: const Brick	c:\Users\jordan\Documents\Visual Studio 2012\Projects\Tetris\Tetris\Level.cpp	55" 

edit: removed the const declaration and it seems to work now. Will try to compile the full program when I get back

[wh1t3crayon]

Odd, now that I removed const in the code above, my console output gives a "!" each time the function is called.

[coder777]

instead of removing const add const to the GetLine() (or GetActiveLine()) function.

But I'd think that this is not the problem. Is it possible that you have dangling references?