vigra - HDF5Handle Class Reference

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| HDF5Handle Class Reference Import/Export of Images and Arrays in HDF5 Format |

Wrapper for unique hid_t objects. More...

`#include <vigra/hdf5impex.hxx>`

## Public Member Functions
herr_t | close ()
| Explicitly call the stored destructor (if one has been registered in the constructor) for the contained handle and set the wrapper to NULL. Returns a negative value when the destructor call for the handle fails, and a non-negative value otherwise.
hid_t | get () const
| Get a temporary hid_t object for the contained handle. Do not call a close function on the return value - a crash will be likely otherwise.
| HDF5Handle ()
| Default constructor. Creates a NULL handle.
| HDF5Handle (hid_t h, Destructor destructor, const char *error_message)
| Create a wrapper for a hid_t object. More...
| HDF5Handle (HDF5Handle const &h)
| Copy constructor. More...
| operator hid_t () const
| Convert to a plain hid_t object. More...
bool | operator!= (HDF5Handle const &h) const
| Inequality comparison of the contained handle.
bool | operator!= (hid_t h) const
| Inequality comparison of the contained handle.
HDF5Handle & | operator= (HDF5Handle const &h)
| Assignment. Calls close() for the LHS handle and hands over ownership of the RHS handle (analogous to `std::unique_pt`).
bool | operator== (HDF5Handle const &h) const
| Equality comparison of the contained handle.
bool | operator== (hid_t h) const
| Equality comparison of the contained handle.
hid_t | release ()
| Return the contained handle and set the wrapper to NULL without calling `close()`.
void | reset (hid_t h, Destructor destructor, const char *error_message)
| Reset the wrapper to a new handle. More...
void | swap (HDF5Handle &h)
| Swap the contents of two handle wrappers. More...
| ~HDF5Handle ()
| Destructor. Calls close() for the contained handle.

## Detailed Description

Wrapper for unique hid_t objects.

This class offers the functionality of `std::unique_ptr` for HDF5 handles (type `hid_t`). Unfortunately, `std::unique_ptr` cannot be used directly for this purpose because it only works with pointers, whereas `hid_t` is an integer type.

Newly created or opened HDF5 handles are stored as objects of type `hid_t`. When the handle is no longer needed, the appropriate close function must be called. However, if a function is aborted by an exception, this is difficult to ensure. Class HDF5Handle is a smart pointer that solves this problem by calling the close function in the destructor (This is analogous to how `std::unique_ptr` calls 'delete' on the contained pointer). A pointer to the close function must be passed to the constructor, along with an error message that is raised when creation/opening fails.

When a `HDF5Handle` is created or assigned from another one, ownership passes on to the left-hand-side handle object, and the right-hand-side objects is resest to a NULL handle.

Since `HDF5Handle` objects are convertible to `hid_t`, they can be used in the code in place of the latter.

Usage:

HDF5Handle file_id(H5Fopen(filename, H5F_ACC_RDWR, H5P_DEFAULT),
&H5Fclose,
"Error message when H5Fopen() fails.");
... // use file_id in the same way as a plain hid_t object
// pass ownership to a new handle object
HDF5Handle new_handle(file_id);
assert(file_id.get() == 0);

#include <vigra/hdf5impex.hxx>
Namespace: vigra

## Constructor & Destructor Documentation

HDF5Handle | ( | hid_t | h,
|  | Destructor | destructor,
|  | const char * | error_message
| ) |  |

Create a wrapper for a hid_t object.

The hid_t object h is assumed to be the return value of an open or create function. It will be closed with the given close function destructor as soon as this HDF5Handle is destructed, except when destructor is a NULL pointer (in which case nothing happens at destruction time). If h has a value that indicates failed opening or creation (by HDF5 convention, this means that h is negative), an exception is raised by calling `vigra_fail(error_message)`.

Usage:

HDF5Handle file_id(H5Fopen(filename, H5F_ACC_RDWR, H5P_DEFAULT),
&H5Fclose,
"Error message.");
... // use file_id in the same way

HDF5Handle | ( | HDF5Handle const & | h | ) |

Copy constructor.

Hands over ownership of the RHS handle (analogous to `std::unique_pt`).

## Member Function Documentation

void reset | ( | hid_t | h,
|  | Destructor | destructor,
|  | const char * | error_message
| ) |  |

Reset the wrapper to a new handle.

Equivalent to `handle = HDF5Handle(h, destructor, error_message)`.

void swap | ( | HDF5Handle & | h | ) |

Swap the contents of two handle wrappers.

Also available as `std::swap(handle1, handle2)`.

operator hid_t | ( |  | ) | const

Convert to a plain hid_t object.

This function ensures that hid_t objects can be transparently replaced with HDF5Handle objects in user code. Do not call a close function on the return value - a crash will be likely otherwise.

The documentation for this class was generated from the following file:

- vigra/hdf5impex.hxx

© Ullrich Köthe (ullrich.koethe@iwr.uni-heidelberg.de) Heidelberg Collaboratory for Image Processing, University of Heidelberg, Germany | html generated using doxygen and Python vigra 1.11.1 (Fri May 19 2017)