I am trying to write code for a block which accepts a vector input and
spits out a vector output. The block is derived from gr_sync_block.
From the tutorial on
OOThttp://gnuradio.org/redmine/projects/gnuradio/wiki/OutOfTreeModules#Adding-the-block-codeI
have the following information. For a block with single input and
single
output the init method is as given below.

Hi,
I am not sure if there are any other types except Complex, Float,
Integer
and Message. But you may wanna look into gr_vector_sink/source_i/f/c.
For
example gr_vector_source_c is a source of gr_complex which gets its data
from a vector where as gr_vector_sink_c is a gr_complex sink which
writes
to a vector. Similarly for int(i) and float(f). May be you can find more
details in doxygen

If I am wrong I hope someone from list will correct me and provide the
right way to do it.