pSOSystem System Calls - Read

select pNA+ System Calls
select Checks the status of multiple sockets.
#include
long select(
int width, /* largest descriptor list */
fd_set *readset, /* read descriptor list */
fd_set *writeset, /* write descriptor list
fd_set *exceptset, /* exception list */
struct timeval *timeout /* timeout for operation */
)
Description
Arguments
This system call is used to multiplex I/O requests among multiple sockets. Three
sets of socket descriptors may be specified: a set of sockets from which to read, a set
to which to write and a set that may have pending exceptional conditions.
Each set is actually a structure containing an array of long integer bit masks. The
size of the array is set by the definition of FD_SETSIZE (in .) The array is
long enough to hold one bit for each FD_SETSIZE socket descriptor.
If select() returns successfully, the three sets indicate which socket descriptors
can be read, which can be written to, or which have exceptional conditions pending.
A timeout value may be specified.
width Specifies the largest descriptor list given by readset, writeset,
or exceptset.
readset Points to a set of sockets from which to read.
writeset Points to a set of sockets to which to write.
exceptset Points to a set of sockets that may have an exceptional condition
pending.
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