__alignof Operator
Microsoft Specific
Returns a value, of type size_t, that is the alignment requirement of the type.
__alignof(
type
)
Remarks
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: