The operator : __alignof( )

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__alignof Operator

Visual Studio .NET 2003

Other Versions

Microsoft Specific

Returns a value, of type size_t, that is the alignment requirement of the type.

Copy

__alignof( type )

For example:

Expression	Value
__alignof( char )	1
__alignof( short )	2
__alignof( int )	4
__alignof( __int64 )	8
__alignof( float )	4
__alignof( double )	8
__alignof( char* )	4

The __alignof value is the same as the value for sizeof for basic types. Consider, however, this example:

typedef struct { int a; double b; } S;
// __alignof(S) == 8

In this case, the __alignof value is the alignment requirement of the largest element in the structure.

Similarly, for

typedef __declspec(align(32)) struct { int a; } S;

__alignof(S) is equal to 32.
One use for __alignof would be as a parameter to one of your own memory-allocation routines. For example, given the following defined structure S, you could call a memory-allocation routine named aligned_malloc to allocate memory on a particular alignment boundary.

typedef __declspec(align(32)) struct { int a; double b; } S;
int n = 50; // array size
S* p = (S*)aligned_malloc(n * sizeof(S), __alignof(S));

For more information on modifying alignment, see:

• pack
• align

END Microsoft Specific

See Also

Expressions with Unary Operators | C++ Keywords