alignof operator (since C++11) - cppreference.com (original) (raw)

Queries alignment requirements of a type.

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[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 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.

[edit] Notes

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

[edit] Keywords

alignof

[edit] Example

#include   struct Foo { int i; float f; char c; };   // Note: alignas(alignof(long double)) below can be // simplified to alignas(long double) if desired. struct alignas(alignof(long double)) Foo2 { // put your definition here };   struct Empty {};   struct alignas(64) Empty64 {};   #define SHOW(expr) std::cout << #expr << " = " << (expr) << '\n'   int main() { SHOW(alignof(char)); SHOW(alignof(int*)); SHOW(alignof(Foo)); SHOW(alignof(Foo2)); SHOW(alignof(Empty)); SHOW(alignof(Empty64)); }

Possible output:

alignof(char) = 1 alignof(int*) = 8 alignof(Foo) = 4 alignof(Foo2) = 16 alignof(Empty) = 1 alignof(Empty64) = 64

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
CWG 1305 C++11 type-id could not represent a reference to an arraywith an unknown bound but a complete element type allowed

[edit] References

[edit] See also