genassym.cf(5) [netbsd man page]

GENASSYM.CF(5)						      BSD File Formats Manual						    GENASSYM.CF(5)

NAME

     genassym.cf -- assym.h definition file

DESCRIPTION

     The genassym.cf file is used by genassym(1) to make constant C expressions known to assembler source files.  Lines starting with '#' are dis-
     carded by genassym(1).  Lines starting with include, ifdef, if, else or endif are preceded with '#' and passed otherwise unmodified to the C
     compiler.	Lines starting with quote get passed on with the quote command removed.  The first word after a define command is taken as a CPP
     identifier and the rest of the line has to be a constant C expression. The output of genassym(1) will assign the numerical value of this
     expression to the CPP identifier.	export X is a shorthand for define X X.  struct X remembers X for the member command and does a define
     X_SIZEOF sizeof(X).  member X does a define X offsetof(<last struct>, X).	config <ctype> <gcc constraint> <asm print modifier> can be used
     to customize the output of genassym(1).  When producing C output, values are casted to <ctype> (default: long) before they get handed to
     printf. <gcc constraint> (default: n) is the constraint used in the __asm__ statements. <asm print modifier> (default: empty) can be used to
     force gcc to output operands in different ways then normal. The "a" modifier e.g. stops gcc from emitting immediate prefixes in front of con-
     stants for the i386 and m68k port.

FILES

     /usr/src/sys/arch/${MACHINE}/${MACHINE}/genassym.cf

SEE ALSO

     genassym(1)

HISTORY

     The genassym.cf file appeared in NetBSD 1.3.

BSD
								  August 18, 2005							       BSD

OFFSETOF(3)						     Linux Programmer's Manual						       OFFSETOF(3)

NAME

       offsetof - offset of a structure member

SYNOPSIS

       #include <stddef.h>

       size_t offsetof(type, member);

DESCRIPTION

       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).

RETURN VALUE

       offsetof() returns the offset of the given member within the given type, in units of bytes.

CONFORMING TO

       C89, C99, POSIX.1-2001.

EXAMPLE

       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=%ld; c=%ld; d=%ld a=%ld
",
		   (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
", (long) sizeof(struct s));

	   exit(EXIT_SUCCESS);
       }

COLOPHON

       This  page is part of release 3.27 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

GNU
								    2008-07-12							       OFFSETOF(3)