Case Sensitive Dictionary Keys

问题:

I've found plenty of info on the web about making dictionaries able to do case insensitive look-ups such that if I added a key/value pair of ("A", "value") calling

MyDict["a"] == MyDict["A"]

will return true.

What I want to know is why I get a "key has already been added" error when I do

MyDict.Add("A", "value1");
MyDict.Add("a", "value2");

if I defined my dictionary to do case sensitive look-ups. Is there no way to define a Dictionary to be able to add different cased keys?

回答1:

Dictionaries are case-sensitive by default - you don't need to do anything.

Dictionary<string, string> myDict = new Dictionary<string, string>();
myDict.Add("A", "value1");
myDict.Add("a", "value2");

See your code working online here: ideone.

If you are getting an error with your code then it's because one of those keys already exist in your dictionary.

回答2:

All Dictionaries are case-sensisitive. But you can use the case-insensitive string comparers provided by the StringComparer class to create dictionaries with case-insensitive string keys.

Check it from ideone.

回答3:

The OP is actually correct if he was using the StringDictionary Class. Microsoft's site states that the key is converted to lower-case before it's stored (https://msdn.microsoft.com/en-us/library/system.collections.specialized.stringdictionary(v=vs.110).aspx). To make the key case sensitive, using the Generic Dictionary as Mark Byers suggested works nicely. If you want a case insensitive key, StringDictionary works well.