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Resizes and, if required, re-allocates memory that will later be freed internally by the HDF5 library


H5_RESIZE_MEMORY(mem, size)


void * H5resize_memory
    void   *mem,
    size_t  size

void *memIN: Pointer to a buffer to be resized
May be NULL
size_t sizeIN: New size of the buffer, in bytes


H5_RESIZE_MEMORY takes a pointer to an existing buffer and resizes the buffer to match the value in size. If necessary, the buffer is reallocated. If size is 0, the buffer is released.

The input buffer must either be NULL or have been allocated by H5_ALLOCATE_MEMORY since the input buffer may be freed by the library.

For certain behaviors, the pointer mem may be passed in as NULL.

This function is intended to have the semantics of realloc():

H5resize_memory(buffer, size)   Resizes buffer.
Returns pointer to resized buffer.
H5resize_memory(NULL, size)Allocates memory using HDF5 Library allocator.
Returns pointer to new buffer
H5resize_memory(buffer, 0)Frees memory using HDF5 Library allocator.
Returns NULL.
H5resize_memory(NULL, 0)Returns NULL (undefined in C standard).

Unlike realloc(), which allows for a “special” pointer to be returned instead of NULL, this function always returns NULL on failure or when size is 0 (zero).

At this time, the only intended use for this function is to resize or reallocate memory that will be returned to the library (and eventually to the user) as a data buffer from a third-party HDF5 filter.

To avoid heap corruption, allocated memory should be freed using the same library that initially allocated it. In most cases, the HDF5 API uses resources that are allocated and freed either entirely by the user or entirely by the library, so this is not a problem. In rare cases, however, HDF5 API calls will free memory that the user allocated. This function allows the user to safely allocate this memory.

It is particularly important to use this function to resize memory on Microsoft Windows systems. In Windows, the C standard library is implemented in dynamic link libraries (DLLs) known as the C run-time (CRT). Each version of Visual Studio comes with multiple versions of the CRT DLLs (debug, release, et cetera) and allocating and freeing memory across DLL boundaries can cause resource leaks and subtle bugs due to heap corruption.

Even when using this function, it is still best to ensure that all components of a C application are built with the same version of Visual Studio and the same configuration (Debug or Release), and thus linked against the same CRT.

Only use this function to resize memory inside third-party HDF5 filters. It will generally not be safe to use this function to resize memory for any other purpose.


On success, returns pointer to resized or reallocated buffer or returns NULL if size is 0 (zero).

Returns NULL on failure.


Coming soon!

See Also:

  • Page:
    H5_ALLOCATE_MEMORY — Allocates memory that will later be freed internally by the HDF5 library

Release    Change
1.8.15C function introduced with this release.

--- Last Modified: July 28, 2020 | 10:16 AM