See if key exists in c++ map

Question

I have a c++ map where the value type is a bool. I need to see if a key exists in the map, and if it doesn't, return false. This is my code right now:

try {
  return board.at[{x, y}];
}
catch (const std::out_of_range& oor) {
  return false;
}

I don't want to use the [] operator because that will initialize the value if it doesn't exist. Is there any way to see if the value exists in the map without a try block?

Or `board.count({x,y}) > 0` (or if you have C++20 `board.contains({x,y})`) — Tyler V, May 11 '20 at 15:28
You can use `find`, if you need the iterator it returns, else use `count`. — nada, May 11 '20 at 15:46

score 2 · Answer 1 · answered May 11 '20 at 15:27

2

You can use std::map::find which will return an iterator the element if found, or .end if not found.

return board.find({x, y}) != board.end();

answered May 11 '20 at 15:27

Cory Kramer

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score 1 · Answer 2 · answered May 11 '20 at 15:27

1

return my_map.count({x, y}) is the idiomatic way, and has the advantage of the implicit bool conversion.

C++20 adds bool contains( const Key& key ) const.

answered May 11 '20 at 15:27

Bathsheba

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See if key exists in c++ map

2 Answers2