alignof operator (since C++11)

Queries alignment requirements of a type

Syntax


`alignof(` type-id `)`

Returns a value of type std::size_t.

Explanation

Returns the alignment, in bytes, required for any instance of the type indicated by type-id, which is either complete object type, an array type whose element type is complete, or a reference type to one of those types.

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.

Keywords

alignof

Notes

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

Example

#include <iostream>
 
struct Foo {
    int   i;
    float f;
    char  c;
};
 
// Note: `alignas(alignof(long double))` below can be simplified to simply 
// `alignas(long double)` if desired.
struct alignas(alignof(long double)) Foo2 {
    // put your definition here
}; 
 
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"
        "- class Foo2       : " << alignof(Foo2)    << "\n"
        "- empty class      : " << alignof(Empty)   << "\n"
        "- alignas(64) Empty: " << alignof(Empty64) << "\n";
}

Possible output:

Alignment of
- char             : 1
- pointer          : 8
- class Foo        : 4
- class Foo2       : 16
- empty class      : 1
- alignas(64) Empty: 64