robgruen's WebLog

For a lowest level hint, analyse the PE header:

// ============================= use at your own risk ===========================
static bool IsClrImage( string fileName )
{
FileStream fs = null;
try
{
fs = new FileStream( fileName, FileMode.Open, FileAccess.Read, FileShare.Read );
byte[] dat = new byte[300];
fs.Read( dat, 0, 128 );
if( (dat[0] != 0x4d) || (dat[1] != 0x5a) ) // "MZ" DOS header
return false;

int lfanew = BitConverter.ToInt32( dat, 0x3c );
fs.Seek( lfanew, SeekOrigin.Begin );
fs.Read( dat, 0, 24 ); // read signature & PE file header
if( (dat[0] != 0x50) || (dat[1] != 0x45) ) // "PE" signature
return false;

fs.Read( dat, 0, 96 + 128 ); // read PE optional header
if( (dat[0] != 0x0b) || (dat[1] != 0x01) ) // magic
return false;

int clihd = BitConverter.ToInt32( dat, 208 ); // get IMAGE_COR20_HEADER rva-address
return clihd != 0;
}
catch( Exception )
{
return false;
}
finally
{
if( fs != null )
fs.Close();
}
}
// ==============================================================================

http://groups.google.de/group/microsoft.public.de.german.entwickler.dotnet.framework/msg/1af0719168e45e84

You don't quite explain in what context this information is required. Programmatically or just while browsing and looking at some DLL? Your answer is fine for the former but for the latter I find it much easier to file up ILDASM and drag and drop the DLL onto it. I will give you an error if its not managed. Alternatively you can have the VC++ tool depends.exe associated with the .DLL extension. Then its just a double click to figure it out. A managed DLL will only be linked against mscoree.dll in the dependency list. Its that simple.