The -genmake option causes a makefile to be generated. The makefile can be used to compile the generated source files to create the asn1api.dll library. User can use the nmake command in Visual Studio .NET command prompt to use this makefile.

When a makefile is generated, it is assumed that the ASN1C project exists within the ASN1C installation directory tree. The generation logic tries to determine the root directory of the installation by traversing upward from the project directory in an attempt to locate the csharp subdirectory which is assumed to be the installation root directory. If the project is located outside of the ASN1C hierarchy, the user can set the OSROOTDIR environment variable to point at the root directory.

If the root directory is located successfully, the generated build script will use that directory; however, if the compiler fails to find the installation root directory, it will use @ROOT_DIR@ instead and print an error message. Users will have to manually replace @ROOT_DIR@ with the actual compiler installation root directory.

If the compiler fails to find the asn1rt.dll runtime library, it will use @ASN1RT_DIR@ instead and print an error message. User will have to manually replace @ASN1RT_DIR@ with the actual C# runtime library directory.