zkSysSelect.h is a portable wrapper for the POSIX header <sys/select.h>. It is part of the libzk library because <sys/select.h> doesn't exist in Standard C.

zkSysSelect.h - Supported Macros from <sys/select.h>
Macro Description
FD_SETSIZE Maximum number of file descriptors in an fd_set structure.

zkSysSelect.h - Supported Types from <sys/select.h>
Type Description
fd_set, a struct with members:  
long fds_bits[]
 

zkSysSelect.h - Supported Functions from <sys/select.h>
FD_CLR
FD_ISSET
FD_SET
FD_ZERO

zkSysSelect.h - Deprecated Functions from <sys/select.h>
Don't Call This Instead, Call This Reason
select zkSelect Not in Standard C. Note that file descriptors can not portably be passed to this function.

zkSysSelect.h - New Functions
ZK_FD_MAXFD1
ZK_FD_MAXFDS