alignof operator (since C++11)

 

C++

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Technical Specifications

 

C++ language

 

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Operators

Assignment operators: a=b, a+=b, a-=b, a*=b, a/=b, a%=b, a&=b, a|=b, a^=b, a<<=b, a>>=

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

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alignof

sizeof

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typeid

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Operator overloading

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Explicit conversions (T)a, T(a)

User-defined conversion

 

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 {};
 
struct alignas(1) Double { 
    double d;    
};
 
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"
        "- alignas(1) Double: " << alignof(Double)  << '\n';
}

Possible output:

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

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)
alignment_of (C++11)	obtains the type's alignment requirements (class template)