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From: mike@turing.UNM.EDU (Michael I. Bushnell)
Newsgroups: comp.lang.c,comp.arch
Subject: Re: Bit Addressable Architectures
Message-ID: <955@unmvax.unm.edu>
Date: 15 Apr 88 06:20:02 GMT
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In article <8646@eleazar.Dartmouth.EDU> major@eleazar.Dartmouth.EDU (Lou Major) writes:

>*ahem*

>char foo[]="This is a test.";

>sizeof (foo) == sizeof (char *)

>NOT the number of machine bytes/words those characters take up. (16, for most
>typical installations)


Perhaps people have had the POINTER == ARRAY thing hammerred into
their skull too hard.  According to the 4.3 BSD "C Programming
Language Reference Manual, page 8 [PS1:1-8]", I find:

  The sizeof operator yeilds the size in bytes of its operand.  (...)
  When applied to an array, the result is the total number of bytes in
  the array.  The size is determined from the declarations of the
  objects in the expression....


But what about the compiler?  Here are the results.

for the code

char foo1[]="This is a test.";
int size1=sizeof foo1;
char *foo2="This is a test.";
int size2=sizeof foo2;

I get:

[4.3 BSD pcc]:

LL0:
	.data
	.data
	.globl	_foo1
_foo1:
	.long	0x73696854
	.long	0x20736920
	.long	0x65742061
	.long	0x2e7473
	.data
	.align	2
	.globl	_size1
_size1:
	.long	16		# NOTE: 16 for the array

	.align	2
	.globl	_foo2
_foo2:
	.data	2
L14:
	.ascii	"This is a test.\0"
	.data
	.long	L14
	.align	2
	.globl	_size2
_size2:
	.long	4		# NOTE: 4 for the pointer




[GNU C Compiler 1.18]:

#NO_APP
.globl _foo1
.data
	.align 0
_foo1:
	.ascii "This is a test.\0"
.globl _size1
.data
	.align 2
_size1:
	.long 16		# NOTE: 16 for the array

.globl _foo2
.text
	.align 0
LC0:
	.ascii "This is a test.\0"
.data
	.align 2
_foo2:
	.long LC0
.globl _size2
.data
	.align 2
_size2:
	.long 4			# NOTE: 4 for the pointer





Plug: Note how much easier it is to read the gcc stuff too...

                N u m q u a m   G l o r i a   D e o 

			Michael I. Bushnell
			HASA - "A" division
14308 Skyline Rd NE				Computer Science Dept.
Albuquerque, NM  87123		OR		Farris Engineering Ctr.
	OR					University of New Mexico
mike@turing.unm.edu				Albuquerque, NM  87131
{ucbvax,gatech}!unmvax!turing.unm.edu!mike