The /cstub switch specifies the name of the client stub file for an RPC interface.
midl /cstub stub_file_name
Specifies a file name that overrides the default client stub file name. File names can be explicitly quoted using double quotes (") to prevent the shell from interpreting the special characters.
The specified file name replaces the default file name. By default, the file name is obtained by adding the extension _c.c to the name of the IDL file. This switch does not affect OLE interfaces.
When you are importing files, the specified file name applies to only one stub file — the stub file that corresponds to the IDL file specified on the command line.
If stub_file_name does not include an explicit path, the file is written to the current directory or the directory specified by the /out switch. An explicit path in stub_file_name overrides the /out switch specification.
The /client none switch takes precedence over the /cstub switch.
midl /cstub my_cstub.c filename.idl