use of subscript([]) operator of map

[Krishanu Debnath]

Hello,

In case the key is not present, map:perator[] returns(and also insert)
a pair with that key and a default value.
Now my question is whether addition of these extra 'unwanted
key' can increase the run time for search operation. I am not sure about
the implementation.

Thanks
Krishanu

 

[Gianni Mariani]

Hello,

In case the key is not present, map:perator[] returns(and also insert)
a pair with that key and a default value.
Now my question is whether addition of these extra 'unwanted
key' can increase the run time for search operation. I am not sure about
the implementation.

Absolutely, but if it is significant is the real question. This depends
on just how many you're inserting and just how sensitive your
application is to that and we have no way of knowing.

 

[Tom Widmer]

Hello,

In case the key is not present, map:perator[] returns(and also insert)
a pair with that key and a default value.
Now my question is whether addition of these extra 'unwanted
key' can increase the run time for search operation. I am not sure about
the implementation.

Yes. Lookup is O(log m.size()), so adding elements slows down lookup.
If you just want to lookup an element then use map::find.

Tom

 

[Andrey Tarasevich]

...
In case the key is not present, map:perator[] returns(and also insert)
a pair with that key and a default value.
Now my question is whether addition of these extra 'unwanted
key' can increase the run time for search operation. I am not sure about
the implementation.
...

Well, it probably does increase the run time. However, I don't exactly
understand your concern. 'std::map<>:perator []' is not a pure search
operation and is not intended to be used as such. 'std::map<>:perator
[]' is a search-and-overwrite operation (hence no const version, BTW).
If you need a pure search operation, use 'std::map<>::find'.