`_aligned_offset_malloc_dbg`

Article
02/07/2023

Allocates memory on a specified alignment boundary (debug version only).

Syntax

void * _aligned_offset_malloc_dbg(
   size_t size,
   size_t alignment,
   size_t offset,
   const char *filename,
   int linenumber
);

Parameters

size
The size of the requested memory allocation.

alignment
The alignment value, which must be an integer power of 2.

offset
The offset into the memory allocation to force the alignment.

filename
Pointer to the name of the source file that requested the allocation operation or NULL.

linenumber
Line number in the source file where the allocation operation was requested or NULL.

Return value

A pointer to the memory block that was allocated or NULL if the operation failed.

Remarks

_aligned_offset_malloc_dbg is a debug version of the _aligned_offset_malloc function. When _DEBUG isn't defined, each call to _aligned_offset_malloc_dbg is reduced to a call to _aligned_offset_malloc. Both _aligned_offset_malloc and _aligned_offset_malloc_dbg allocate a block of memory in the base heap, but _aligned_offset_malloc_dbg offers several debugging features: buffers on either side of the user portion of the block to test for leaks, and filename/linenumber information to determine the origin of allocation requests. Tracking specific allocation types with a block type parameter isn't a supported debug feature for aligned allocations. Aligned allocations will appear as a _NORMAL_BLOCK block type.

_aligned_offset_malloc_dbg allocates the memory block with slightly more space than the requested size. The extra space is used by the debug heap manager to link the debug memory blocks and to provide the application with debug header information and overwrite buffers. When the block is allocated, the user portion of the block is filled with the value 0xCD, and each of the overwrite buffers are filled with 0xFD.

_aligned_offset_malloc_dbg is useful in situations where alignment is needed on a nested element; for example, if alignment was needed on a nested class.

_aligned_offset_malloc_dbg is based on malloc; for more information, see malloc.

This function sets errno to ENOMEM if the memory allocation failed or if the requested size was greater than _HEAP_MAXREQ. For more information about errno, see errno, _doserrno, _sys_errlist, and _sys_nerr. Also, _aligned_offset_malloc validates its parameters. If alignment isn't a power of 2, or if offset is non-zero and greater than or equal to size, this function invokes the invalid parameter handler, as described in Parameter validation. If execution is allowed to continue, this function returns NULL and sets errno to EINVAL.

For information about how memory blocks are allocated, initialized, and managed in the debug version of the base heap, see CRT debug heap details.

For information about the allocation block types and how they're used, see Types of blocks on the debug heap.

Requirements

Routine	Required header
`_aligned_offset_malloc_dbg`	<crtdbg.h>

For more compatibility information, see Compatibility.

Libraries

Debug versions of C run-time libraries only.

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