Upon successful completion a pointer is returned;
this pointer becomes invalid after the next
I/O
operation on
stream
(whether successful or not)
or as soon as the stream is closed.
Otherwise,
NULL
is returned.
The
fgetwln()
function
does not distinguish between end-of-file and error; the routines
feof(3)
and
ferror(3)
must be used
to determine which occurred.
If an error occurs, the global variable
errno
is set to indicate the error.
The end-of-file condition is remembered, even on a terminal, and all
subsequent attempts to read will return
NULL
until the condition is
cleared with
clearerr(3).
The text to which the returned pointer points may be modified,
provided that no changes are made beyond the returned size.
These changes are lost as soon as the pointer becomes invalid.