offsetof – cppreference.com

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definiert in Header `<cstddef>`

`#define offsetof(type, member) /implementation-defined/`

Die Makro offsetof expandiert zu einer Konstante vom Typ std::size_t, deren Wert von den Offset in Bytes vom Anfang eines Objekts der angegebenen Typs in ihren angegebenen Elements einschließlich der Polsterung gegebenenfalls .. ist

Original:

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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Notes

Wenn type nicht ein Standard-Layout-Typ, ist das Verhalten undefiniert .

Original:

If type is not a standard-layout type, the behavior is undefined.

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Wenn member ein statisches Element oder ein Funktionselement ist, ist das Verhalten undefiniert .

Original:

If member is a static member or a function member, the behavior is undefined.

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Die des ersten Teils eines Standard-Tastaturbelegung Offset ist immer Null (empty-base-Optimierung ist obligatorisch)

Original:

The offset of the first member of a standard-layout type is always zero (empty-base-Optimierung is mandatory)

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Mögliche Implementierung

#define offsetof(type,member) ((std::size_t) &(((type*)0)->member))

Beispiel

#include <iostream>
#include <cstddef>
struct S {
    char c;
    double d;
};
int main()
{
    std::cout << "the first element is at offset " << offsetof(S, c) << '\n'
              << "the double is at offset " << offsetof(S, d) << '\n';
}

Output:

the first element is at offset 0
the double is at offset 8

Siehe auch


	vorzeichenloser Ganzzahltyp, der vom Operator `sizeof` zurückgegeben wird Original: unsigned integer type returned by the `sizeof` operator The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (typedef) [edit]

	prüft, ob ein Typ ist Standard-Layout-Typ Original: checks if a type is standard-layout type The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (Klassen-Template) [edit]