Variable sized message in MPI

Question

Is there a library call that would allow for sending/receiving of variable sized messages using MPI?

A work around would be to send the data size in the first message and follow it with the actual payload, but I was wondering if there was a convention for combining these two separate messages.

Answer 1

The count provided to MPI_Recv is only an upper bound. MPI_Get_count can be used to find the exact number of items received.

Kind of like sockets I guess.