Is there a way to convert "int" to typeof(int) in c#?

Question

I know that I can obtain a type from string name like so

Type intType = Type.GetType("System.Int32");

But, what if I have string like so

string[] typeNameArr = new string[] {"Int", "String", "DateTime", "Bool"};

How to convert these to actual types? Maybe I can get full qualified name out of an alias and then do the GetType?

You could add your own `if` conditions to always evaluate "Int" as "System.Int32". — Standard_101, May 26 '21 at 10:08
Your array of strings is odd. `Int` needs to become either `int` or `System.Int32`, whereas `DateTime` needs to become `System.DateTime` (there's no DateTime language alias). I think you're going to have to special-case some of these -- have a look-up which knows about `Int` etc, and just try prepending `System.` to those which aren't in your lookup — canton7, May 26 '21 at 10:09
@canton7 I know. But even if its "int" can I convert it to typeof(int) dynamically without using a hard coded if else? — Talha, May 26 '21 at 10:12
Sounds like you basically want a `Dictionary` - add every type you know about from the web service to that dictionary. — Jon Skeet, May 26 '21 at 10:12
@Talha Even if you can convert it to `int`, you'll need to manually map that to `System.Int32` in order to use it with `Type.GetType` — canton7, May 26 '21 at 10:13
@JonSkeet I thought of that. But I was wondering if I can do it dynamically via reflection or so. Predefined dictionary would be my last option. — Talha, May 26 '21 at 10:14
Also, instantiating arbitrary types based on deserialized data is a **huge security hole**. There are types hiding away in the BCL which will do arbitrary things when they're instantiated, and attackers can use this to perform remote code execution. You **must** white-list any sort of object creation to just known-safe types — canton7, May 26 '21 at 10:14
@canton7 Don't we have anything where we can get a type by using alias string only? — Talha, May 26 '21 at 10:15
No. The alias is a C# language concept, but `Type.GetType` is provided by the runtime and is used for all CLR languages — canton7, May 26 '21 at 10:16
Do you actually have that much variation in the type? Just writing the dictionary is faster than fiddling with reflection. — Martheen, May 26 '21 at 10:16

Stefan · Answer 1 · 2021-05-26T10:56:51.273

6

If you use fully qualified names, like "System.Int32" in the end you'll be able to to it through linq:

var types = typeNameArr.Select(c => Type.GetType(c));

Additionally: if your web-service provide custom names, you either need a mapping or a convention. E.g.:

var types = typeNameArr.Select(c => Type.GetType("System." + c));

or

var types = typeNameArr.Select(c => 
{
   switch (c)
   {
      "Int":
          return typeof(int);
      "Foo":
          return typeof(BarClass);  
      default:
          return  null
   }        
});

edited May 26 '21 at 10:56

answered May 26 '21 at 10:08

Stefan

17,448
11
60
79

I am getting this array from a WebService so I cannot use fully qualified names here. I need a dynamic way of correctly converting these to actual c# types. – Talha May 26 '21 at 10:09
1

@Talha: But `Int` is neither a .NET Type (that would be `System.Int32`) nor a C# alias (that would be `int` with a lowercase `i`)! Thus, I'm afraid you'll have to hard-code a conversion table yourself (for example, with a large switch statement). – Heinzi May 26 '21 at 10:10
@Heinzi I know. But that I can change to lowercase. – Talha May 26 '21 at 10:11
3

@Talha: Since the [list of C# aliases](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/built-in-types) fairly short and unlikely to change, I would definitely argue for a large, hard-coded `switch` statement rather than using some framework magic. – Heinzi May 26 '21 at 10:13
2

You might as well do a mapping from `string` to `Type` at this point: `c switch { "Int" => typeof(int), ... }` – canton7 May 26 '21 at 10:21

score 3 · Answer 2 · answered May 26 '21 at 10:33

To get all primitive types with their alias you can write:

string assemblyFullName = "mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089";
var assembly = Assembly.Load(assemblyFullName);
var primitiveTypes =
    assembly.DefinedTypes.Where(definedType => definedType.IsPrimitive && definedType != typeof(IntPtr) && definedType != typeof(UIntPtr));

using (var provider = new CSharpCodeProvider())
{
    var result = primitiveTypes.Select(x => (Alias: provider.GetTypeOutput(new CodeTypeReference(x)), Type: x));
}

Would result in:

bool    typeof(Boolean)
byte    typeof(Byte)
char    typeof(Char)
double  typeof(Double)
short   typeof(Int16)
int     typeof(Int32)
long    typeof(Int64)
sbyte   typeof(SByte)
float   typeof(Single)
ushort  typeof(UInt16)
uint    typeof(UInt32)
ulong   typeof(UInt64)

What to do with `DateTime`? Why the answer and not just a comment with reference to [this](https://stackoverflow.com/q/59005990/1997232) or [this](https://stackoverflow.com/q/2442534/1997232)? — Sinatr, May 26 '21 at 11:19
Just add a manual mapping for it. Adding a manual mapping for all the types might very well be the best solution, just wanted to show that it could also be done using code. — Magnus, May 26 '21 at 17:48

Is there a way to convert "int" to typeof(int) in c#?

2 Answers2