Unnecessary parentheses (Was: Help: VAX C problem)

[Stephen Clamage]

sadkins at oucsace.cs.OHIOU.EDU (Scott W. Adkins) writes:

>Let us clarify the sizeof operator/function a little bit more.  I cannot
>say that this is strictly K&R, because I can't....
>Quoting from "Using Turbo C" by Herbert Schildt,

>"Turbo C includes the compile-time operator called sizeof that returns the 
>size of the variable of type that is its operand.  The keyword sizeof precedes
>the operand's variable or type name.  If sizeof operates on a data type, then
>the type must appear in parentheses."

>In this case, they do not indicate that one is a function and the other is 
>an operator.  Would someone please help me out here.  Is this specific to 
>IBM PC's or is it part of standard C?

In the ANSI C specification (section 3.3.3 and 3.3.3.4), sizeof is called
a unary operator.  Its operand is either a unary-expression or a type-name
in parentheses.  "unary-expression" and "type-name" are further defined
elsewhere in the grammar.  Among other kinds of expressions, any
expression enclosed in parens is a unary-expression, so you can always
use parens.  For example:
	int i;
	char c;
	sizeof c + i	/* A */
	sizeof (c) + i	/* B */
	sizeof (c + i)	/* C */
The values of A and B are the same, since sizeof operates on c.  The
result of sizeof on a char type is guaranteed to be 1 by the language.
In C, however, the entire expression (c+i) is the operand of sizeof,
the type of the expression is int, and the result of sizeof on an int
is whatever the implementation says it is, typically 2 or 4.
Now consider:
	sizeof(char)	/* guaranteed to be 1 */
	sizeof char	/* syntax error */
	sizeof( (int*)[10] )	/* array of 10 pointers to int */
For types, the parens are required as part of the syntax, independent
of whatever parens the type description may require.
-- 

Steve Clamage, TauMetric Corp, steve at taumet.com