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How to tell if a map element exists?

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Started by Mizipzor July 04, 2005 08:13 AM

2 comments, last by Zahlman 18 years, 9 months ago

Mizipzor

247

Author

July 04, 2005 08:13 AM

Hi there, my texture name (string) are represented by chars so I can use them in chararrays as tilemaps. It looks like this:


std::map <char, std::string> BmpRef; // so we know which string(texture) is represented by which char

Then we got the function to retrieve which string is tied to which char:


std::string FindBmpRef(char a) {return BmpRef[a];}; // find which string is represented by the specified char

But what about if the char (a) doesnt exists in the map? Then I want to return the string "UNDEFINED". How do I check for a map element? Couldnt find it in the msdn...

289

July 04, 2005 08:17 AM

map::find

returns an iterator with the passed in key. if it doesn't exist returns equivalent to end()

"Absorb what is useful, reject what is useless, and add what is specifically your own." - Lee Jun Fan

Mizipzor

247

Author

July 04, 2005 08:22 AM

Thanks, I wrote the function like this:

std::string	Sdl_handle::FindBmpRef(char a) {	if( BmpRef.find(a) == BmpRef.end() ) {		return "UNDEFINED";	} 	else		return BmpRef[a];}

Does it look ok to you?

Zahlman

1,682

July 04, 2005 01:31 PM

In case you are wondering, if the key is not present, the [] operator will return a default-constructed value - and also insert that key-value pair (with the new key and the default value). For std::string, that would mean a default of an empty string (zero-length). Which is easy enough to check for, but the extra insertions are undesirable :/

How to tell if a map element exists?

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How to tell if a map element exists?

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