# Return Code of API Functions

Most of API functions return common result code as enum type `FRESULT`. When an API function succeeded, it returns zero (`FR_OK`), otherwise it returns non-zero value indicates type of error.

FR_OK (0)
  The function succeeded.
FR_DISK_ERR
  The lower layer, `disk_read`, `disk_write` or `disk_ioctl` function, reported that an unrecoverable hard error occured.
  Note that if once this error occured at any operation to an open file, the file object is aborted and all operations to the file except for close will be rejected.
FR_INT_ERR
  Assertion failed. An insanity is detected in the internal process. One of the following possibilities is suspected.
  - Work area (file system object, file object or etc...) has been broken by stack overflow or any other tasks. This is the reason in most case.
  - There is an error of the FAT structure on the volume.
  - There is a bug in the FatFs module itself.
  Note that if once this error occured at any operation to an open file, the file object is aborted and all operations to the file except for close will be rejected.
FR_NOT_READY
  The lower layer, `disk_initialize` function, reported that the storage device could not be got ready to work. One of the following possibilities is suspected.
  - No medium in the drive.
  - Wrong lower layer implementation for the storage device.
  - Wrong hardware configuration.
  - The storage device is broken.
FR_NO_FILE
  Could not find the file.
FR_NO_PATH
  Could not find the path.
FR_INVALID_NAME
  The given string is invalid as the path name.
FR_DENIED
  The required access was denied due to one of the following reasons:
  - Write mode open against the read-only file.
  - Deleting the read-only file or directory.
  - Deleting the non-empty directory or current directory.
  - Reading the file opened without `FA_READ` flag.
  - Any modification to the file opened without `FA_WRITE` flag.
  - Could not create the object due to root directory full or disk full.
  - Could not allocate a contiguous area to the file.
FR_EXIST
  Name collision. An object with the same name is already existing.
FR_INVALID_OBJECT
  The file/directory object is invalid or a null pointer is given. There are some reasons as follows:
  - It has been closed, it has not been opened or it has been collapsed.
  - It has been invalidated by a voulme mount process. Open objects on the volume are invalidated by voulme mount process.
  - Physical drive is not ready to work due to a media removal.
FR_WRITE_PROTECTED
  A write mode operation against the write-protected media.
FR_INVALID_DRIVE
  Invalid drive number is specified in the path name. A null pointer is given as the path name. (Related option: `FF_VOLUMES`)
FR_NOT_ENABLED
  Work area for the logical drive has not been registered by `f_mount` function.
FR_NO_FILESYSTEM
  There is no valid FAT volume on the drive.
FR_MKFS_ABORTED
  The `f_mkfs` function aborted before start in format due to a reason as follows:
  - It is pmpossible to formart with the given parameters.
  - The size of volume is too small.
  - The size of given work area is too small.
  - The partition bound to the logical drive coulud not be found. (Related option: `FF_MULTI_PARTITION`)
FR_TIMEOUT
  The function was canceled due to a timeout of thread-safe control. (Related option: `FF_TIMEOUT`)
FR_LOCKED
  The operation to the object was rejected by file sharing control. (Related option: `FF_FS_LOCK`)
FR_NOT_ENOUGH_CORE
  Not enough memory for the operation. There is one of the following reasons:
  - Could not allocate a memory for LFN working buffer. (Related option: `FF_USE_LFN`)
  - Size of the given buffer is insufficient for the size required.
FR_TOO_MANY_OPEN_FILES
  Number of open objects has been reached maximum value and no more object can be opened. (Related option: `FF_FS_LOCK`)
FR_INVALID_PARAMETER
  The given parameter is invalid or there is an inconsistent for the volume.

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