F.4. Creating DLL assemblies using csc.exe

If you are using csc.exe, you will need to know how to reference classes coded in other assemblies using the /reference option.

Let's say you have two classes, called MyClass1 and MyClass2, in separate source files. ^[4] MyClass1 creates a new instance of MyClass2 in its Main method.

^[4] Of course, you can put them into the same source file and no referring will be required. But I am trying to show how you can reference something coded in another source file (which will eventually be compiled into a separate assembly).

1: // MyClass1.cs
2: public class MyClass1{
3:   public static void Main(){
4:     MyClass2 mc2 = new MyClass2();
5:     System.Console.WriteLine(mc2.Add(3,4));
6:   }
7: }

1: // MyClass2.cs – in separate source file
2: public class MyClass2{
3:   public int Add (int a, int b){
4:     return a + b;
5:   }
6: }

You need to compile MyClass2.cs into a DLL assembly. It cannot be an EXE assembly since it doesn't contain a Main method, and hence isn't 'executable'.

Use the /target:library ^[5] option to compile MyClass2.cs into MyClass2.dll:

^[5] You can use /t instead of /target. /t is a shortcut.

c:expt>csc /target:library MyClass2.cs

When you compile MyClass1.cs, make sure you reference MyClass2.dll like this:

c:expt>csc /reference:MyClass2.dll MyClass1.cs

Try compiling without the /reference:MyClass2.dll switch and the compiler will complain that MyClass2 is an unknown symbol.

You can reference multiple DLLs when compiling a single C# source file by separating them with commas:

/reference:MyClass2.dll,MyClass3.dll,MyClass4.dll.

You can also combine multiple source files into a single DLL assembly. The following command will compile both source files and put the resultant IL codes into a single DLL assembly called MyClass2.dll:

c:expt>csc /target:library MyClass2.cs MyClass3.cs