Declared in rt_sys.h, the
_sys_istty() function determines whether a file handle is attached to an interactive device.
The Arm® libraries call
__sys_istty() to determine whether a file handle (that is
being used for an output file stream) is attached to an interactive device.
For file streams that are attached to interactive devices, the Arm library:
- Provides unbuffered behavior by default, in the absence of a call to
- Prohibits seeking.
stderrare assumed to be interactive devices. They are line-buffered at program startup, regardless of what
_sys_isttyreports for them. An exception is if they have been redirected on the command line.
NoteThis restriction does not apply when using microlib. In microlib,
stderrare always unbuffered.
The return value is one of the following values:
fhis not attached to an interactive device.
fhis attached to an interactive device.
- An error occurred.