String casts in .NET

Question

Why is there so may ways to convert to a string in .net? The ways I have seen are .ToString, Convert.ToString() and (string). What is the Difference.

Answer 1

ToString() is a method of object, and it will always work on a non-null reference, so you'll get something, but whether that something is what you want, is a different story.

Convert.ToString() will yield the same result in most cases, but isn't as flexible as Object.ToString() as you can't pass custom formatting rules.

(string) will cast your object to string, and if it isn't a string then you'll get an InvalidCastException().

Answer 2

object.ToString() is the most basic way of retrieving a string representation of an object, and can be specifically implemented by the object.

Convert.ToString() expands on that and provides some specific overloads for primitive types (char, byte, int, double, etc.) that allow for some more type-specific functionality (like base conversion, for example)

(string) is a casting operator, and will only work if the type is either a string or has an implicit or explicit operator that can convert it to a string. Otherwise you'll get an InvalidCastException

Answer 3

• .ToString() can be called from any object. However, if the type you call it on doesn't have a good implementation the default is to return the type name rather than something meaningful about the instance of that type. This method is inherited from the base Object type, and you can overload it in your own types to do whatever you want.

• (string) is a cast, not a function call. You should only use this if the object you need already is a string in some sense, or if you know there is a good implicit conversion available (like from int). This will throw an exception is the object cannot be converted (including when the object is null)

• as string is another way to write (string), but it differs in that it returns null rather than throwing an exception if the cast fails.

• Convert.ToString() attempts to actually convert the argument into a string. This is the best option if you don't really know much about the argument. It can be slow because it has to do a lot of extra work to determine what kind of results to return, but that same work also makes it the most robust option when you don't know very much about the argument. If nothing else is available, it will fall back to calling the argument's .ToString() method.

• String.Format The string class' .Format method can also be used to convert certain types to strings, with the additional advantage that you have some control over what the resulting string will look like.

• Serialization This is a little more complicated, but .Net includes a couple different mechanisms for converting objects into a representation that can be safely stored and re-loaded from disk or other streaming mechanism. That includes a binary formatter, but most often involves converting to a string in some format or other (often xml). Serialization is appropriate when you want to later convert the your string back into it's originating type, or if you want a complete representation of a complex type.

Answer 4

Don't forget as string

Answer 5

Convert.ToString() will return an empty string if the object is null .ToString and (String) will throw an exception. Convert.ToString will internally call .ToString() if the value is null it will return an empty String.

Answer 6

.ToString() is an instance method which asks the object for its string representation. When the object is null, this will throw a exception.

(string) is a cast to the string type, which isn't a very good idea in most cases except for simple data types, since it can break (throw an exception) when it's null or an invalid cast

Convert.ToString() does a bit more checking than a simple cast, giving a more robust alternative to the cast. It will return the empty string when the object is null.