[FreeRTOS+FAT Standard API Reference]
long ff_ftell( FF_FILE *pxStream );
Returns the current read/write position of an open file in the embedded FAT file system. The position is returned as the number of bytes from the start of the file.
|pxStream||The file being queried. The file must have first been opened using a call to ff_fopen().|
If pxStream is not NULL then the file’s current read/write position is returned. The returned value is the number of bytes the file’s read/write position is from the start of the file.
If pxStream is NULL then -1 is returned.