POSIX API
6-3 FILE ACCESS FUNCTIONS
The file access functions provide an API for performing a sequence of operations on a file
located on a volume’s file system. The file object pointer returned when a file is opened is
passed as an argument of all file access function, and the file object so referenced maintains
information about the actual file (on the volume) and the state of the file access. The file
access state includes the file position (the next place data will be read/written), error
conditions and (if file buffering is enabled) the state of any file buffer.
As data is read from or written to a file, the file position is incremented by the number of
bytes transferred from/to the volume. The file position may also be directly manipulated by
the application using the position set function ( fs_fsetpos() ), and the current absolute
file position may be gotten with the position get function ( fs_fgetpos() ), to be later used
with the position set function.
Closed
Open
Read
Error
Clear error
Ready
Must be
Closed
Write
Reading
Write
(file at EOF)
Writing
Figure 6-1 File state transitions.
86
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