I'm calling IMetadataImport.EnumUserStrings from managed code and it's
returning me garbage strings.
I've converted the the interface method in managed code this way:

void EnumUserStrings(
ref IntPtr phEnum,
[Out, MarshalAs(UnmanagedType.LPWStr)] StringBuilder rStrings,
[In] uint cmax,
out uint pcStrings);

I always set the cmax value to 0.  Here is the code that calls it

ArrayList userStrings = new ArrayList();
StringBuilder rStrings = new StringBuilder();
IntPtr phEnum = IntPtr.Zero;
uint pcStrings = 0;

try {
this.IMetaDataImport.EnumUserStrings( ref phEnum, rStrings, 1, out
pcStrings );
while (pcStrings != 0) {
 userStrings.Add( rStrings.ToString() );

 this.IMetaDataImport.EnumUserStrings( ref phEnum, rStrings, 1, out
pcStrings );

}

return userStrings;
}

finally {
this.IMetaDataImport.CloseEnum( phEnum );

}

Did anyone tried this in managed code and know what I'm doing wrong?