H5F: File Interface

File API Functions

The C Interfaces:

H5Fcreate H5Fopen H5Freopen H5Fclose

H5Fflush H5Fis_hdf5 H5Fmount H5Funmount

H5Fget_vfd_handle H5Fget_create_plist H5Fget_access_plist H5Fget_obj_count H5Fget_obj_ids

The FORTRAN90 Interfaces:
In general, each FORTRAN90 subroutine performs exactly the same task as the corresponding C function. The links below go to the C function descriptions, which serve as general descriptions for both. A button, under Non-C API(s) at the end of the C function description, opens an external browser window displaying the FORTRAN90-specific information. You will probably want to adjust the size and location of this external window so that both browser windows are visible and to facilitate moving easily between them.

h5fcreate_f h5fopen_f h5freopen_f h5fclose_f

h5fflush_f h5fis_hdf5_f h5fmount_f h5funmount_f

h5fget_vfd_handle_f h5fget_create_plist_f h5fget_access_plist_f h5fget_obj_count_f h5fget_obj_ids_f

Name: H5Fopen

Signature:

hid_t H5Fopen(const char *name, unsigned flags, hid_t access_id )

Purpose:

Opens an existing file.

Description:

H5Fopen opens an existing file and is the primary function for accessing existing HDF5 files.

The parameter access_id is a file access property list identifier or H5P_DEFAULT if the default I/O access parameters are to be used

The flags argument determines whether writing to an existing file will be allowed. The file is opened with read and write permission if flags is set to H5F_ACC_RDWR. All flags may be combined with the bit-wise OR operator (`|') to change the behavior of the file open call. More complex behaviors of file access are controlled through the file-access property list.

The return value is a file identifier for the open file; this file identifier should be closed by calling H5Fclose when it is no longer needed.

Special case -- Multiple opens:
A file can often be opened with a new H5Fopen call without closing an already-open identifier established in a previous H5Fopen or H5Fcreate call. Each such H5Fopen call will return a unique identifier and the file can be accessed through any of these identifiers as long as the identifier remains valid. In such multiply-opened cases, all the open calls should use the same flags argument.

In some cases, such as files on a local Unix file system, the HDF5 library can detect that a file is multiply opened and will maintain coherent access among the file identifiers.

But in many other cases, such as parallel file systems or networked file systems, it is not always possible to detect multiple opens of the same physical file. In such cases, HDF5 will treat the file identifiers as though they are accessing different files and will be unable to maintain coherent access. Errors are likely to result in these cases. While unlikely, the HDF5 library may not be able to detect, and thus report, such errors.

It is generally recommended that applications avoid multiple opens of the same file.

Parameters:

const char *name

IN: Name of the file to access.

unsigned flags

IN: File access flags. Allowable values are:

H5F_ACC_RDWR

Allow read and write access to file.

H5F_ACC_RDONLY

Allow read-only access to file.

• H5F_ACC_RDWR and H5F_ACC_RDONLY are mutually exclusive; use exactly one.
• An additional flag, H5F_ACC_DEBUG, prints debug information. This flag is used only by HDF5 library developers; it is neither tested nor supported for use in applications.

hid_t access_id

IN: Identifier for the file access properties list. If parallel file access is desired, this is a collective call according to the communicator stored in the access_id. Use H5P_DEFAULT for default file access properties.

Returns:

Returns a file identifier if successful; otherwise returns a negative value.

Non-C API(s):

Name: H5Fcreate

Signature:

hid_t H5Fcreate(const char *name, unsigned flags, hid_t create_id, hid_t access_id )

Purpose:

Creates HDF5 files.

Description:

H5Fcreate is the primary function for creating HDF5 files .

The flags parameter determines whether an existing file will be overwritten. All newly created files are opened for both reading and writing. All flags may be combined with the bit-wise OR operator (`|') to change the behavior of the H5Fcreate call.

The more complex behaviors of file creation and access are controlled through the file-creation and file-access property lists. The value of H5P_DEFAULT for a property list value indicates that the library should use the default values for the appropriate property list.

The return value is a file identifier for the newly-created file; this file identifier should be closed by calling H5Fclose when it is no longer needed.

Special case -- File creation in the case of an already-open file:
If a file being created is already opened, by either a previous H5Fopen or H5Fcreate call, the HDF5 library may or may not detect that the open file and the new file are the same physical file. (See H5Fopen regarding the limitations in detecting the re-opening of an already-open file.)

If the library detects that the file is already opened, H5Fcreate will return a failure, regardless of the use of H5F_ACC_TRUNC.

If the library does not detect that the file is already opened and H5F_ACC_TRUNC is not used, H5Fcreate will return a failure because the file already exists. Note that this is correct behavior.

But if the library does not detect that the file is already opened and H5F_ACC_TRUNC is used, H5Fcreate will truncate the existing file and return a valid file identifier. Such a truncation of a currently-opened file will almost certainly result in errors. While unlikely, the HDF5 library may not be able to detect, and thus report, such errors.

Applications should avoid calling H5Fcreate with an already opened file.

Parameters:

const char *name

IN: Name of the file to access.

uintn flags

IN: File access flags. Allowable values are:

H5F_ACC_TRUNC

Truncate file, if it already exists, erasing all data previously stored in the file.

H5F_ACC_EXCL

Fail if file already exists.

H5F_ACC_TRUNC and H5F_ACC_EXCL are mutually exclusive; use exactly one.

An additional flag, H5F_ACC_DEBUG, prints debug information. This flag is used only by HDF5 library developers; it is neither tested nor supported for use in applications.

hid_t create_id

IN: File creation property list identifier, used when modifying default file meta-data. Use H5P_DEFAULT for default file creation properties.

hid_t access_id

IN: File access property list identifier. If parallel file access is desired, this is a collective call according to the communicator stored in the access_id. Use H5P_DEFAULT for default file access properties.

Returns:

Returns a file identifier if successful; otherwise returns a negative value.

Non-C API(s):

Name: H5Fflush

Signature:

herr_t H5Fflush(hid_t object_id, H5F_scope_t scope )

Purpose:

Flushes all buffers associated with a file to disk.

Description:

H5Fflush causes all buffers associated with a file to be immediately flushed to disk without removing the data from the cache.

object_id can be any object associated with the file, including the file itself, a dataset, a group, an attribute, or a named data type.

scope specifies whether the scope of the flushing action is global or local. Valid values are

H5F_SCOPE_GLOBAL		Flushes the entire virtual file.
H5F_SCOPE_LOCAL		Flushes only the specified file.

Note:

HDF5 does not possess full control over buffering. H5Fflush flushes the internal HDF5 buffers then asks the operating system (the OS) to flush the system buffers for the open files. After that, the OS is responsible for ensuring that the data is actually flushed to disk.

Parameters:

hid_t object_id

IN: Identifier of object used to identify the file.

H5F_scope_t scope

IN: Specifies the scope of the flushing action.

Returns:

Returns a non-negative value if successful; otherwise returns a negative value.

Non-C API(s):

Name: H5Fis_hdf5

Signature:

htri_t H5Fis_hdf5(const char *name )

Purpose:

Determines whether a file is in the HDF5 format.

Description:

H5Fis_hdf5 determines whether a file is in the HDF5 format.

Parameters:

const char *name

IN: File name to check format.

Returns:

When successful, returns a positive value, for TRUE, or 0 (zero), for FALSE. Otherwise returns a negative value.

Non-C API(s):

Name: H5Fget_access_plist

Signature:

hid_t H5Fget_access_plist(hid_t file_id)

Purpose:

Returns a file access property list identifier.

Description:

H5Fget_access_plist returns the file access property list identifier of the specified file.

See "File Access Properties" in H5P: Property List Interface in this reference manual and "File Access Property Lists" in Files in the HDF5 User's Guide for additional information and related functions.

Parameters:

hid_t file_id

IN: Identifier of file to get access property list of

Returns:

Returns a file access property list identifier if successful; otherwise returns a negative value.

Non-C API(s):

Name: H5Fget_create_plist

Signature:

hid_t H5Fget_create_plist(hid_t file_id )

Purpose:

Returns a file creation property list identifier.

Description:

H5Fget_create_plist returns a file creation property list identifier identifying the creation properties used to create this file. This function is useful for duplicating properties when creating another file.

See "File Creation Properties" in H5P: Property List Interface in this reference manual and "File Creation Properties" in Files in the HDF5 User's Guide for additional information and related functions.

Parameters:

hid_t file_id

IN: Identifier of the file to get creation property list of

Returns:

Returns a file creation property list identifier if successful; otherwise returns a negative value.

Non-C API(s):

Name: H5Fget_obj_count

Signature:

herr_t H5Fget_obj_count(hid_t file_id, unsigned int types, unsigned int *obj_id_count )

Purpose:

Returns the number of open object identifiers for an open file.

Description:

Given the identifier of an open file, file_id, and the desired object types, types, H5Fget_obj_count returns the number of open object identifiers for the file.

To retrieve a count of open identifiers for open objects in all HDF5 application files that are currently open, pass the value H5F_OBJ_ALL in file_id.

The types of objects to be counted are specified in types as follows:

H5F_OBJ_FILE	Files only
H5F_OBJ_DATASET	Datasets only
H5F_OBJ_GROUP	Groups only
H5F_OBJ_DATATYPE	Named datatypes only
H5F_OBJ_ALL	All of the above (I.e., H5F_OBJ_FILE | H5F_OBJ_DATASET | H5F_OBJ_GROUP | H5F_OBJ_DATATYPE )

Multiple object types can be combined with the logical OR operator (|). For example, the expression (H5F_OBJ_DATASET|H5F_OBJ_GROUP) would call for datasets and groups.

Parameters:

hid_t file_id

IN: Identifier of a currently-open HDF5 file or H5F_OBJ_ALL for all currently-open HDF5 files.

unsigned int types

IN: Type of object for which identifiers are to be returned.

unsigned int *obj_id_count

OUT: Pointer to the returned list of open object identifiers.

Returns:

Returns a file access property list identifier if successful; otherwise returns a negative value.

Non-C API(s):

Name: H5Fget_obj_ids

Signature:

herr_t H5Fget_obj_ids(hid_t file_id, unsigned int types, hid_t *obj_id_list )

Purpose:

Returns a list of open object identifiers.

Description:

Given the file identifier file_id and the type of objects to be identified, types, H5Fget_obj_ids returns the list of identifiers for all open HDF5 objects fitting the specified criteria.

To retrieve identifiers for open objects in all HDF5 application files that are currently open, pass the value H5F_OBJ_ALL in file_id.

The types of object identifiers to be retrieved are specified in types using the codes listed for the same parameter in H5Fget_obj_count

Parameters:

hid_t file_id

IN: Identifier of a currently-open HDF5 file or H5F_OBJ_ALL for all currently-open HDF5 files.

unsigned int types

IN: Type of object for which identifiers are to be returned.

hid_t *obj_id_list

OUT: Pointer to the returned list of open object identifiers.

Returns:

Returns a non-negative value if successful; otherwise returns a negative value.

Non-C API(s):

Name: H5Fget_vfd_handle

Signature:

herr_t H5Fget_vfd_handle(hid_t file_id, hid_t fapl_id, void *file_handle )

Purpose:

Returns pointer to the file handle from the virtual file driver.

Description:

Given the file identifier file_id and the file access property list fapl_id, H5Fget_vfd_handle returns a pointer to the file handle from the low-level file driver currently being used by the HDF5 library for file I/O.

Notes:

Users are not supposed to modify any file through this file handle.

This file handle is dynamic and is valid only while the file remains open; it will be invalid if the file is closed and reopened or opened during a subsequent session.

Parameters:

hid_t file_id

IN: Identifier of the file to be queried.

hid_t fapl_id

IN: File access property list identifier. For most drivers, the value will be H5P_DEFAULT. For the FAMILY or MULTI drivers, this value should be defined through the property list functions: H5Pset_family_offset for the FAMILY driver and H5Pset_multi_type for the MULTI driver.

void *file_handle

OUT: Pointer to the file handle being used by the low-level virtual file driver.

Returns:

Returns a non-negative value if successful; otherwise returns a negative value.

Name: H5Fclose

Signature:

herr_t H5Fclose(hid_t file_id )

Purpose:

Terminates access to an HDF5 file.

Description:

H5Fclose terminates access to an HDF5 file by flushing all data to storage and terminating access to the file through file_id.

If this is the last file identifier open for the file and no other access identifier is open (e.g., a dataset identifier, group identifier, or shared datatype identifier), the file will be fully closed and access will end.

Delayed close:
Note the following deviation from the above-described behavior. If H5Fclose is called for a file but one or more objects within the file remain open, those objects will remain accessible until they are individually closed. Thus, if the dataset data_sample is open when H5Fclose is called for the file containing it, data_sample will remain open and accessible (including writable) until it is explicitely closed. The file will be automatically closed once all objects in the file have been closed.

Be warned, hoever, that there are circumstances where it is not possible to delay closing a file. For example, an MPI-IO file close is a collective call; all of the processes that opened the file must close it collectively. The file cannot be closed at some time in the future by each process in an independent fashion. Another example is that an application using an AFS token-based file access privilage may destroy its AFS token after H5Fclose has returned successfully. This would make any future access to the file, or any object within it, illegal.

In such situations, applications must close all open objects in a file before calling H5Fclose. It is generally recommended to do so in all cases.

Parameters:

hid_t file_id

IN: Identifier of a file to terminate access to.

Returns:

Returns a non-negative value if successful; otherwise returns a negative value.

Non-C API(s):

Name: H5Fmount

Signature:

herr_t H5Fmount(hid_t loc_id, const char *name, hid_t child_id, hid_t plist_id )

Purpose:

Mounts a file.

Description:

H5Fmount mounts the file specified by child_id onto the group specified by loc_id and name using the mount properties plist_id.

Note that loc_id is either a file or group identifier and name is relative to loc_id.

Parameters:

hid_t loc_id

IN: Identifier for of file or group in which name is defined.

const char *name

IN: Name of the group onto which the file specified by child_id is to be mounted.

hid_t child_id

IN: Identifier of the file to be mounted.

hid_t plist_id

IN: Identifier of the property list to be used.

Returns:

Returns a non-negative value if successful; otherwise returns a negative value.

Non-C API(s):

Name: H5Funmount

Signature:

herr_t H5Funmount(hid_t loc_id, const char *name )

Purpose:

Unmounts a file.

Description:

Given a mount point, H5Funmount dissassociates the mount point's file from the file mounted there. This function does not close either file.

The mount point can be either the group in the parent or the root group of the mounted file (both groups have the same name). If the mount point was opened before the mount then it is the group in the parent; if it was opened after the mount then it is the root group of the child.

Note that loc_id is either a file or group identifier and name is relative to loc_id.

Parameters:

hid_t loc_id

IN: File or group identifier for the location at which the specified file is to be unmounted.

const char *name

IN: Name of the mount point.

Returns:

Returns a non-negative value if successful; otherwise returns a negative value.

Non-C API(s):

Name: H5Freopen

Signature:

hid_t H5Freopen(hid_t file_id )

Purpose:

Returns a new identifier for a previously-opened HDF5 file.

Description:

H5Freopen returns a new file identifier for an already-open HDF5 file, as specified by file_id. Both identifiers share caches and other information. The only difference between the identifiers is that the new identifier is not mounted anywhere and no files are mounted on it.

Note that there is no circumstance under which H5Freopen can actually open a closed file; the file must already be open and have an active file_id. E.g., one cannot close a file with H5Fclose (file_id) then use H5Freopen (file_id) to reopen it.

The new file identifier should be closed by calling H5Fclose when it is no longer needed.

Parameters:

hid_t file_id

IN: Identifier of a file for which an additional identifier is required.

Returns:

Returns a new file identifier if successful; otherwise returns a negative value.

Non-C API(s):