String.empty v.s. string.null

Question

Hello everyone I am doing input parameter checking for a string type and string value except empty is valid. My function is provided to outer client to call. Sometimes I find to check null is not enough I also need to check String.Empty. My question is what are the differences between null and String.Empty? I have made some web search for the answers but not very useful information. thanks in advance George

George George · Answer

Thanks Brandon Great reply! Two more comments 1. In your pseudo code of Empty property each time a new instance is returned right? So references to String.Empty are pointing to different memory locations right? 2. And since the property is a read-only property there is no chance of modifying it and messing anything else up in the application. -- if the property is not read-only what actions you could do to analyze? regards George

George George · Answer

Hi Dave I am interested in your solution -- With 3.5 you can declare and use pointers (just like C++) inside an unsafe block. Theoretically initialise a couple of pointers to strings which are initialised to String.Empty. Could you show your code please? So that all of us could learn from you. regards George

Brandon Lewis · Answer

Good point Dave I sometimes forget just how powerful unsafe code can be in C#. I should try that

Dave · Answer

Whether it points to the same location in memory could probably be checked by someone running the latest version of the .NET framework. With 3.5 you can declare and use pointers (just like C++) inside an unsafe block. Theoretically initialise a couple of pointers to strings which are initialised to String.Empty. Then send those addresses to output. I'm still on 2.0. So I cannot help.

Brandon Lewis · Answer

That's actually a pretty good question and I'm inclined to say yes. Seeing as how a static member is basically a Singleton member of a non-static class like string  String .Empty would be a  global  property and the string object is a reference type (versus a value type for most numerical data objects) then all references to it would point to the same location in memory. Maybe that's why I was always taught to use String .Empty instead of just  because using  allocates new memory while String .Empty does not. I could be wrong though but following what I know about static classes and properties I wanna say that this theory is correct. Of course the property could also look likes something crazy like this: public unsafe static string Empty { get { char tempChar = ' '; return new string (&tempChar); } } Its hard to say what goes on in there... this is why Im going back and learning C++ so I can get a better understanding of the C# language. And since the property is a read-only property there is no chance of modifying it and messing anything else up in the application.

George George · Answer

Thanks Brandon! Great! I found Empty is a static member of String class so it means all string type variables initialized with String.Empty are pointing to the same thing? regards George

Brandon Lewis · Answer

A null string is a string that has not been initialized. It is a string variable that hasn't even been given some memory to store data. This will create a null string: string myString; //Without initializing it will create a null string. An empty string is a string that has been initialized and given some memory but it just doesn't contain any characters (except a null terminator at the end but you don't see that) so as far as the compiler and you are concerned it is a string with a length of 0. string myString = String .Empty; //Will create an empty string. If you want to check for both a null and empty string use the static method proved by the String class: if ( String .IsNullOrEmpty(myString)) { //do something }