notused - >C_id
defines an argument which is not used in the command line mode.
We have always C_id = NULL when the module function is called
in the command line mode.
Therefore, a value NULL means a call from the library.
C_id is a C variable of type pointer to a scalar (e.g. char *),
or a C variable of MegaWave2 type (e.g.
notusedbeing a keyword, you cannot use it elsewhere.