offsetof
From cppreference.com
Defined in header
<cstddef>
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#define offsetof(type, member) /*implementation-defined*/
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The macro offsetof expands to a constant of type std::size_t, the value of which is the offset, in bytes, from the beginning of an object of specified type to its specified member, including padding if any.
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[edit] Notes
If type
is not a standard-layout type, the behavior is undefined.
If member
is a static member or a function member, the behavior is undefined.
The offset of the first member of a standard-layout type is always zero (empty-base optimization is mandatory)
[edit] Possible implementation
#define offsetof(type,member) ((std::size_t) &(((type*)0)->member)) |
[edit] Example
Output:
the first element is at offset 0 the double is at offset 8
[edit] See also
unsigned integer type returned by the sizeof operator (typedef) |
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(C++11)
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checks if a type is standard-layout type (class template) |