[#BloombergLP-bslma-BufferAllocator-allocateFromBuffer-03]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bslma.adoc[bslma]::xref:BloombergLP/bslma/BufferAllocator.adoc[BufferAllocator]::allocateFromBuffer
:relfileprefix: ../../../
:mrdocs:

Allocate a memory block of the specified `size` from `buffer` with the specified `alignment`.

== Synopsis

Declared in `<bslma_bufferallocator.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
static
void*
allocateFromBuffer(
    int* cursor,
    char* buffer,
    xref:BloombergLP/bslma/Allocator/size_type.adoc[size_type] bufSize,
    xref:BloombergLP/bslma/Allocator/size_type.adoc[size_type] size,
    int alignment);
----

== Description

Allocate a memory block of the specified `size` from the specified `buffer` at the specified `cursor` position using the specified `alignment`. Return the address of the allocated memory block if `buffer` contains enough available memory, and `null` otherwise. The `cursor` is set to the index of the next available byte in `buffer` after the allocation. If `size` is 0, do not allocate memory and return zero. The behavior is undefined unless `0 <= bufSize`, `0 <= size`, `0 < alignment <= bsls::AlignmentUtil::BSLS_MAX_ALIGNMENT`, and alignment is an integral power of 2.

== Return Value

address of the allocated block, or null if insufficient space

== Parameters

[cols="1,4"]
|===
| Name| Description
| *cursor*
| Index of the next available byte in `buffer` (in/out).
| *buffer*
| Memory buffer from which to allocate.
| *bufSize*
| Size (in bytes) of `buffer`.
| *size*
| Number of bytes to allocate.
| *alignment*
| Alignment (in bytes) for the allocated block.
|===


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