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 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.

Keywords

alignof

Notes

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

Example

Run this code

#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

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)
Filesystem library (C++17)
Technical Specifications

General
value categories (lvalue, rvalue, xvalue)
order of evaluation (sequence points)
constant expressions
unevaluated expressions
primary expressions
lambda-expression(C++11)
Literals
integer literals
floating-point literals
boolean literals
character literals including escape sequences
string literals
null pointer literal(C++11)
user-defined literal(C++11)
Operators
Assignment operators: `a=b`, `a+=b`, `a-=b`, `a*=b`, `a/=b`, `a%=b`, `a&=b`, `a\|=b`, `a^=b`, `a<<=b`, `a>>=b`
Increment and decrement: `++a`, `--a`, `a++`, `a--`
Arithmetic operators: `+a`, `-a`, `a+b`, `a-b`, `a*b`, `a/b`, `a%b`, `~a`, `a&b`, `a\|b`, `a^b`, `a<<b`, `a>>b`
Logical operators: `a\|\|b`, `a&&b`, `!a`
Comparison operators: `a==b`, `a!=b`, `a<b`, `a>b`, `a<=b`, `a>=b`
Member access operators: `a[b]`, `a`, `&a`, `a->b`, `a.b`, `a->b`, `a.*b`
Other operators: `a(...)`, `a,b`, `a?b:c`
Alternative representations of operators
Precedence and associativity
Fold expression(C++17)
new-expression
delete-expression
throw-expression
alignof
sizeof
sizeof...(C++11)
typeid
noexcept(C++11)
Operator overloading
Conversions
Implicit conversions
const_cast
static_cast
reinterpret_cast
dynamic_cast
Explicit conversions `(T)a`, `T(a)`
User-defined conversion