NAME
offsetof —
offset of a structure member
SYNOPSIS
#include
<stddef.h>
size_t
offsetof(type,
member);
DESCRIPTION
Theoffsetof()
macro expands to an integer constant expression of type
size_t and yields the offset, in bytes, of the field
member from the start of the structure
type.
A compiler error will result if member is not aligned to a byte boundary (i.e. it is a bit-field).
EXAMPLES
Regardless of the architecture and the ABI, the following example prints the value zero for the variable x.
struct example {
double x;
int y;
char z;
};
size_t x, y, z;
x = offsetof(struct example, x);
y = offsetof(struct example, y);
z = offsetof(struct example, z);
(void)printf("%zu %zu %zu\n", x, y, z);
SEE ALSO
STANDARDS
The offsetof() macro conforms to
ANSI X3.159-1989
(“ANSI C89”).