AccessMode and CreationMode

The following table illustrates the behavior of DiskStorage::create/DiskStorageWithRollback::create of each AccessMode and CreationMode combination.

AccessMode	CreationMode	Description	When the file exists	When the file not exist
accessRead	creationDefault	Identical to openExisting	Open it	Fail
	openExisting	If the file exists, opening it in read-only mode. If the file does not exist, the function fails.	Open it	Fail
	openAlways	If the file exists, opening it in read-only mode. If the file does not exist, the function automatically create a new file and open it in read-only mode.	Open it	Create New
	createNew	If the file already exists, the function fails. If the file does not exist, the function creates a new file and open it in read-only mode.	Fail	Create New
	createAlways	The function always create a new file and open it in read-only mode. (Not frequently used.)	Truncate it	Create New
	truncateExisting	If the file exists, the function removes all the content of it and opening it in read-only mode. If the file does not exist, the function fails.	Fail	Fail
accessWrite	creationDefault	Identical to createAlways	Truncate it	Create New
	openExisting	If the file exists, opening it in write-only mode. If the file does not exist, the function fails.	Open it (to overwrite)	Fail
	openAlways	If the file exists, the function open it in write-only mode. If the file does not exist, the function create a new file and open it in write-only mode.	Open it (to overwrite)	Create New
	createNew	If the file already exists, the function fails. If the file does not exist, the function creates a new file and open it in write-only mode.	Fail	Create New
	createAlways	The function always create a new file and open it in write-only mode.	Truncate it	Create New
	truncateExisting	If the file exists, the function removes all the content of it and opening it in write-only mode. If the file does not exist, the function fails.	Truncate it	Fail
accessRW	creationDefault	Identical to openAlways	Open it (to overwrite)	Create New
	openExisting	If the file exists, opening it in read-write mode. If the file does not exist, the function fails.	Open it (to overwrite)	Fail
	openAlways	If the file exists, the function open it in read-write mode. If the file does not exist, the function create a new file and open it in read-write mode.	Open it (to overwrite)	Create New
	createNew	If the file already exists, the function fails. If the file does not exist, the function creates a new file and open it in read-write mode.	Fail	Create New
	createAlways	The function always create a new file and open it in read-write mode.	Truncate it	Create New
	truncateExisting	If the file exists, the function removes all the content of it and opening it in read-write mode. If the file does not exist, the function fails.	Truncate it	Fail

The terms used in 'When the file exists' and 'When the file not exist' are defined as follows:

Fail	The function will fail with the specified parameter configuration.
Open it	The function will open the file.
Open it (to overwrite)	The function will open the file to write on it.
Create New	The function will create a new file.
Truncate it	The function will remove all the contents on the file and open it.

See Also

DiskStorage, StorageRollback, AccessMode, CreationMode