object obj = "Hello";
string str1 = (string)obj;
string str2 = obj.ToString();
What is the difference between (string)obj and obj.ToString()?
asked Oct 14, 2009 at 9:02
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6As I mentioned in my comment to Guillaume, this has nothing to do with boxing. String is a reference type - there's no need for boxing.Jon Skeet– Jon Skeet2009-10-14 09:09:21 +00:00Commented Oct 14, 2009 at 9:09
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1Possible duplicate of Casting vs Converting an object toString, when object really is a stringJim Fell– Jim Fell2016-05-24 17:35:49 +00:00Commented May 24, 2016 at 17:35
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5 Answers
(string)objcastsobjinto astring.objmust already be astringfor this to succeed.obj.ToString()gets a string representation ofobjby calling theToString()method. Which isobjitself whenobjis astring. This (should) never throw(s) an exception (unlessobjhappens to benull, obviously).
So in your specific case, both are equivalent.
Note that string is a reference type (as opposed to a value type). As such, it inherits from object and no boxing ever occurs.
5 Comments
Yannick Motton
One thing to note is that obj, str1 and str2 all reference the same object. So Explicitly casting an object that is a string into a string, will return the objectreference itself.
Yannick Motton
An object doesn't necessarily have to be a string for it to succeed. It also works if there is an explicit conversion operator defined.
Mac
You are obviously right about the conversion operator. But for the sake of non confusion, I'll keep it in the comments. Thanks for pointing this out.
Rodolfo
if obj is null then ToString() will throw a exception.
derekantrican
Rodolfo is correct - if
obj is null (even if it is a null string) then obj.ToString() will throw an exception. Instead, you can use obj?.ToString() which will produce the same effect and not throw an exception if obj is nullIf its any help, you could use the 'as' operator which is similar to the cast but returns null instead of an exception on any conversion failure.
string str3 = obj as string;
1 Comment
Muhammad Musavi
Good point, here is for ones who want to read more about it.
At the most basic level:
(string)obj will attempt to cast obj to a string and will fail if there's no valid conversion.
obj.ToString() will return a string that the designer of obj has decided represents that object. By default it returns the class name of obj.
Comments
(string)obj cast the object and will fail if obj is not null and not a string.
obj.ToString() converts obj to a string (even if it is not a string), it will fail is obj is null as it's a method call.
Comments
ToString() is object class method (the main parent class in .net) which can be overloaded in your class which inherits from object class even if you didn't inherited from it.
(string) is casting which can be implemented in the class it self, the string class so you don't have ability on it.
