_Alignof operator
Queries the alignment requirement of its operand type.
Used when the alignment requirement of its operand type must be known.
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[edit] Syntax
_Alignof( type-name )
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Returns a value of type (an unsigned integer type) size_t.
[edit] Explanation
Yields the alignment requirement of its operand type.
[edit] Notes
Depending on the computer architecture, a byte may consist of 8 or more bits, the exact number being recorded in CHAR_BIT.
_Alignof cannot be used with function types or incomplete types.
When applied to an array type, the result is the alignment requirement of the element type.
When applied to an operand that has structure or union type, the result is the alignment requirement of the member type with the strictest alignment requirement.
[edit] Keywords
[edit] Example
The example output corresponds to a system with 64-bit pointers and 32-bit int.
#include <stdio.h> int main(void) { /* Array */ printf("_Alignof(float[10]) = %zu\n", _Alignof(float[10])); /* Structure */ struct ints_1 { unsigned short int usi; unsigned int ui; unsigned long int uli; unsigned long long int ulli; }; printf("_Alignof(struct ints_1) = %zu\n", _Alignof(struct ints_1)); /* Union */ union ints_2 { unsigned short int usi; unsigned int ui; unsigned long int uli; unsigned long long int ulli; }; printf("_Alignof(union ints_2) = %zu\n", _Alignof(union ints_2)); }
Possible output:
_Alignof(float[10]) = 4 _Alignof(struct ints_1) = 8 _Alignof(union ints_2) = 8
[edit] See also
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C++ documentation for alignof
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