The standard installation of ArgoUML does not support C++, php and C# code generation. To make this possible, you need to download the auxiliary modules from the download page at the ArgoUML website.

Unpack the downloaded file in the same directory as you unpacked ArgoUML itself.

The result should be that the directory that contains the argouml.jar file, now also contains a subdirectory named ext, which contains the .jar files for the extra languages.