How can I determine if a .NET assembly was built for x86 or x64?

Just for clarification, CorFlags.exe is part of the .NET Framework SDK. I have the development tools on my machine, and the simplest way for me determine whether a DLL is 32-bit only is to:

1. Open the Visual Studio Command Prompt (In Windows: menu Start/Programs/Microsoft Visual Studio/Visual Studio Tools/Visual Studio 2008 Command Prompt)

2. CD to the directory containing the DLL in question

3. Run corflags like this: corflags MyAssembly.dll

You will get output something like this:

Microsoft (R) .NET Framework CorFlags Conversion Tool.  Version  3.5.21022.8
Copyright (c) Microsoft Corporation.  All rights reserved.

Version   : v2.0.50727
CLR Header: 2.5
PE        : PE32
CorFlags  : 3
ILONLY    : 1
32BIT     : 1
Signed    : 0

As per comments the flags above are to be read as following:

• Any CPU: PE = PE32 and 32BIT = 0
• x86: PE = PE32 and 32BIT = 1
• 64-bit: PE = PE32+ and 32BIT = 0

Just write your own. The core of the PE architecture hasn't been seriously changed since its implementation in Windows 95.

Here's a C# example:

    public static ushort GetPEArchitecture(string pFilePath)
    {
        ushort architecture = 0;
        try
        {
            using (System.IO.FileStream fStream = new System.IO.FileStream(pFilePath, System.IO.FileMode.Open, System.IO.FileAccess.Read))
            {
                using (System.IO.BinaryReader bReader = new System.IO.BinaryReader(fStream))
                {
                    // Check the MZ signature
                    if (bReader.ReadUInt16() == 23117)
                    {
                        // Seek to e_lfanew.
                        fStream.Seek(0x3A, System.IO.SeekOrigin.Current);

                        // Seek to the start of the NT header.
                        fStream.Seek(bReader.ReadUInt32(), System.IO.SeekOrigin.Begin);

                        if (bReader.ReadUInt32() == 17744) // Check the PE\0\0 signature.
                        {
                            // Seek past the file header,
                            fStream.Seek(20, System.IO.SeekOrigin.Current);

                            // Read the magic number of the optional header.
                            architecture = bReader.ReadUInt16();
                        }
                    }
                }
            }
        }
        catch (Exception) { /* TODO: Any exception handling you want
                                     to do, personally I just take 0
                                     as a sign of failure */
        }

        // If architecture returns 0, there has been an error.
        return architecture;
    }
}

Now the current constants are:

0x10B - PE32  format.
0x20B - PE32+ format.

But with this