alignof operator (since C++11)

< cpp‎ | language

Queries alignment requirements of a type


[edit] Syntax

alignof( type-id )

Returns a value of type std::size_t.

[edit] Explanation

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.

[edit] Keywords


[edit] Notes

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

[edit] Example

#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

[edit] 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) [edit]
obtains the type's alignment requirements
(class template) [edit]