alignof operator (since C++11)

Queries alignment requirements of a type.


alignof( type-id )

Returns a value of type std::size_t.


Returns the alignment, in bytes, required for any instance of the type indicated by type-id, which is either complete type, an array type, or a reference type.

If the type is reference type, the operator returns the alignment of referenced type; if the type is array type, alignment requirement of the element type is returned.




See alignment for the meaning and properties of the value returned by alignof.


#include <iostream>
struct Foo {
    int   i;
    float f;
    char  c;
struct Empty {};
struct alignas(64) Empty64 {};
int main()
    std::cout << "Alignment of"  "\n"
        "- char             : " << alignof(char)    << "\n"
        "- pointer          : " << alignof(int*)    << "\n"
        "- class Foo        : " << alignof(Foo)     << "\n"
        "- empty class      : " << alignof(Empty)   << "\n"
        "- alignas(64) Empty: " << alignof(Empty64) << "\n";

Possible output:

Alignment of
- char             : 1
- pointer          : 8
- class Foo        : 4
- empty class      : 1
- alignas(64) Empty: 64

See also

alignment requirement restricts the addresses at which an object may be allocated
alignas specifier specifies that the storage for the variable should be aligned by specific amount (C++11)
obtains the type's alignment requirements
(class template)

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