astChannelDataastChannelData - Return a pointer to user-supplied data stored with a Channel

Description:
This macro is intended to be used within the source or sink functions associated with a ChannelChannel. It returns any pointer previously stored in the Channel (that is, the Channel that has invoked the source or sink function) using astPutChannelDataastPutChannelData.

This mechanism is a thread-safe alternative to passing file descriptors, etc, via static global variables.

Synopsis:
void $*$astChannelData
Class Applicability:
Channel
This macro applies to all Channels.
Returned Value:
astChannelData
The pointer previously stored with the Channel using astPutChannelData. A NULL pointer will be returned if no such pointer has been stored with the Channel.
Notes:
  • This routine is not available in the Fortran 77 interface to the AST library.