I dunno if strings work and from the manual it seems it can take integer/float
values only.So you could try :-

-d var1

...

IFDEF var1;
{
str_cpy(my_str,"foobar");
}

I haven't tried it,but let me know if it works !
Secondly,how can a value given by -d be directly
accesed via C-script ?

I like good 'views' because they have no 'strings' attached..