offsetof(3) — Справочная страница Linux
offsetof(3) Library Functions Manual offsetof(3)
НАЗВАНИЕ
offsetof - offset of a structure member
БИБЛИОТЕКА
Standard C library (libc, -lc)
СИНТАКСИС
#include <stddef.h>
size_t offsetof(type, member);
ОПИСАНИЕ
The macro offsetof() returns the offset of the field member from
the start of the structure type.
This macro is useful because the sizes of the fields that compose
a structure can vary across implementations, and compilers may
insert different numbers of padding bytes between fields.
Consequently, an element's offset is not necessarily given by the
sum of the sizes of the previous elements.
A compiler error will result if member is not aligned to a byte
boundary (i.e., it is a bit field).
ЗНАЧЕНИЕ, ВОЗВРАЩАЕМОЕ ФУНКЦИЕЙ
offsetof() returns the offset of the given member within the
given type, in units of bytes.
СТАНДАРТЫ
C11, POSIX.1-2008.
ИСТОРИЯ
POSIX.1-2001, C89.
ПРИМЕРЫ
On a Linux/i386 system, when compiled using the default gcc(1)
options, the program below produces the following output:
$ ./a.out
offsets: i=0; c=4; d=8 a=16
sizeof(struct s)=16
Program source
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
int
main(void)
{
struct s {
int i;
char c;
double d;
char a[];
};
/* Output is compiler dependent */
printf("offsets: i=%zu; c=%zu; d=%zu a=%zu\n",
offsetof(struct s, i), offsetof(struct s, c),
offsetof(struct s, d), offsetof(struct s, a));
printf("sizeof(struct s)=%zu\n", sizeof(struct s));
exit(EXIT_SUCCESS);
}
КОЛОФОН
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user-space interface documentation) project. Information about
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⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
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2024-06-26. If you discover any rendering problems in this HTML
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Linux man-pages 6.9.1 2024-06-15 offsetof(3)
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