.\" CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
.\" TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
.\" SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
-.\" %%%END_LICENSE
+.\" %%%LICENSE_END
.\"
.\" References:
.\" /usr/lib/gcc/i486-linux-gnu/4.1.1/include/stddef.h
.\" glibc-doc
-.TH OFFSETOF 3 2008-07-12 "GNU" "Linux Programmer's Manual"
+.TH OFFSETOF 3 2019-03-06 "GNU" "Linux Programmer's Manual"
.SH NAME
offsetof \- offset of a structure member
.SH SYNOPSIS
.nf
.B #include <stddef.h>
-.sp
+.PP
.BI "size_t offsetof(" type ", " member );
.fi
.SH DESCRIPTION
The macro
.BR offsetof ()
returns the offset of the field
-\fImember\fP from the start of the structure \fItype\fP.
-
+.I member
+from the start of the structure
+.IR type .
+.PP
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.
-
+.PP
A compiler error will result if
-\fImember\fP is not aligned to a byte boundary
+.I member
+is not aligned to a byte boundary
(i.e., it is a bit field).
.SH RETURN VALUE
.BR offsetof ()
.IR type ,
in units of bytes.
.SH CONFORMING TO
-C89, C99, POSIX.1-2001.
+POSIX.1-2001, POSIX.1-2008, C89, C99.
.SH EXAMPLE
On a Linux/i386 system, when compiled using the default
.BR gcc (1)
options, the program below produces the following output:
+.PP
.in +4n
-.nf
-
+.EX
.RB "$" " ./a.out"
offsets: i=0; c=4; d=8 a=16
sizeof(struct s)=16
-.fi
+.EE
+.in
.SS Program source
\&
-.nf
+.EX
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
/* Output is compiler dependent */
- printf("offsets: i=%ld; c=%ld; d=%ld a=%ld\\n",
- (long) offsetof(struct s, i),
- (long) offsetof(struct s, c),
- (long) offsetof(struct s, d),
- (long) offsetof(struct s, a));
- printf("sizeof(struct s)=%ld\\n", (long) sizeof(struct s));
+ printf("offsets: i=%zd; c=%zd; d=%zd a=%zd\en",
+ offsetof(struct s, i), offsetof(struct s, c),
+ offsetof(struct s, d), offsetof(struct s, a));
+ printf("sizeof(struct s)=%zd\en", sizeof(struct s));
exit(EXIT_SUCCESS);
}
-.fi
+.EE