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POSIX API
The file maintains flags that reflect errors encountered in the previous file access, and
subsequent accesses will fail (under certain conditions outlined here) unless these flags are
explicitly cleared (using fs_clearerr() ). There are actually two sets of flags. One reflects
whether the file encountered the end-of-file (EOF) during the previous access, and if this is
set, writes will not fail, but reads will fail. The other reflects device errors, and no
subsequent file access will succeed (except file close) unless this is first cleared. The
functions fs_ferror() and fs_feof() can be used to get the state of device error and
EOF conditions, respectively.
If file buffering is enabled ( FS_CFG_FILE_BUF_EN is DEF_ENABLED ), then input/output
buffering capabilities can be used to increase the efficiency of file reads and writes. A buffer
can be assigned to a file using fs_setbuf() or fs_setvbuf() ; the contents of the buffer
can be flushed to the storage device using fs_fflush() .
If a file is shared between several tasks in an application, a file lock can be employed to
guarantee that a series of file operations are executed atomically. fs_flockfile() (or its
non-blocking equivalent fs_ftrylockfile() ) acquires the lock for a task (if it does not
already own it). Accesses from other tasks will be blocked until a fs_funlockfile() is
called. This functionality is available if FS_CFG_FILE_LOCK_EN is DEF_ENABLED .
6-3-1 OPENING, READING & WRITING FILES
When an application needs to access a file, it must first open it using fs_fopen():
file pointer -->
p_file = fs_fopen(“\\file.txt”, <-- file name
“w+”); <-- mode string
if (p_file == (FS_FILE *)0) {
/* $$$$ Handle error */
}
The return value of this function should always be verified as non-NULL before the
application proceeds to access the file. The first argument of this function is the path of the
file; if working directories are disabled, this must be the absolute file path, beginning with
either a volume name or a ‘\’ (see section 4-3 “μC/FS File and Directory Names and Paths”
on page 62). The second argument of this function is a string indicating the mode of the
file; this must be one of the strings shown in the table below. Note that in all instances, the
‘b’ (binary) option has no affect on the behavior of file accesses.
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