Vala-Problem with stdout and pipe

[Matthias Huber]

Sorry when i am nervy, but i don't find a documentation about vala's stdout:

when i pipe my program (because i don't want to rewrite my c-code 
completele with vala)
into my program, or even into tail, the prog doesn't show any output with my

stdout.printf("sonemting")

is there a stdout.flush() ?
yes there is one.

but that doesn't help me.

Any Idea ?