The f_expand function prepares or allocates a contiguous data area to the file. When opt is 1, the function allocates a contiguous data area to the file. Unlike expansion of file by f_lseek function, the file must be truncated prior to use this function and read/write pointer of the file stays at top of the file after the function. The file content allocated with this function is undefined because no data is written to the file in this process. The function can fail with FR_DENIED due to some reasons below.
+The f_expand function prepares or allocates a contiguous data area to the file. When opt is 1, the data area is allocated to the file in this function. Unlike expansion of file size by f_lseek function, the file must be truncated prior to use this function and read/write pointer of the file stays at offset 0 after the function call. The file content allocated with this function is undefined, because no data is written to the file in this process. The function can fail with FR_DENIED due to some reasons below.
When opt is 0, the function finds a contiguous data area and set it as suggested point for next allocation instead of allocating it to the file. The next cluster allocation is started at top of the contiguous area found by this function. Thus the write file is guaranteed be contiguous and no allocation delay until the size reaches that size at least unless any other changes to the volume is performed.
-The contiguous file would have an advantage at time-critical read/write operations. It eliminates some overheads in the filesystem and the storage media caused by random access due to fragmented file data. Especially FAT access for the contiguous file on the exFAT volume is completely eliminated and storage media will be accessed sequentially.
-Also the contiguous file can be easily accessed directly via low-level disk functions. But this is not recommended in consideration for future compatibility.
+When opt is 0, the function finds a contiguous data area and set it as suggested point for next allocation. The subsequent cluster allocation begins at top of the contiguous area found by this function. Thus the file allocation is guaranteed be contiguous and without allocation delay until the file size reaches this size unless any other changes to the volume is performed.
+The contiguous file has an advantage for time-critical read/write operations. It eliminates some overheads in the filesystem and the storage device caused by random access for fragmented file.
+Also the contiguous file can be easily accessed directly via low-level disk functions. However, this is not recommended in consideration of portability and future compatibility. If the file has not been confirmed be contiguous, use this function to examine if the file is contiguous or not.