C# Error CS2034 – A /reference option that declares an extern alias can only have one filename. To specify multiple aliases or filenames, use multiple /reference options.

C# Error

CS2034 – A /reference option that declares an extern alias can only have one filename. To specify multiple aliases or filenames, use multiple /reference options.

Reason for the Error & Solution

A /reference option that declares an extern alias can only have one filename. To specify multiple aliases or filenames, use multiple /reference options.

To specify two aliases and/or file names, use two /reference options, like this:

Example

The following code will generate error CS2034.

// CS2034.cs  
// compile with: /r:A1=cs2034a1.dll;A2=cs2034a2.dll  
// to fix, compile with: /r:A1=cs2034a1.dll /r:A2=cs2034a2.dll  
// CS2034  
extern alias A1;  
extern alias A2;  
using System;