Submission Date: 10 Dec 92
Submittor: WG14
Source: X3J11/91-046 (Kuo-Wei Lee)
Question 1
Under subclause 6.8.3.1 Argument substitution, the C Standard states
on page 90, lines 12-14:
Before being substituted, each argument's preprocessing tokens are completely macro replaced as if they form the rest of the translation unit; no other preprocessing tokens are available.
It is not clear to us what should happen if, after the first replacement,
the argument is a valid preprocessing number. Consider the following example:
#define X 0x000E
#define Y 0x0100
#define FOO(a) a
FOO(X+Y)
After X is replaced, FOO(X+Y)
becomes FOO(0x000E+Y). At this point, should the macro
replacement continue and expand Y to be 0x0100 with the
final result being FOO(0x000E+0x0100); or should the expansion
stop since 0x000E+Y is a syntactically valid preprocessing
number?
In other words, should FOO(X+Y) be expanded into FOO(0x000E+0x0100),
or should it be FOO(0x000E+Y)?
Response
Subclause 5.1.1.2, page 5, lines 32-39 indicate that translation must proceed
as if all creation of preprocessing tokens completes before any macro expansion
begins. These are translation phases 3 and 4:
3. The source file is decomposed into preprocessing tokens and sequences of white-space characters (including comments)...Therefore, if X+Y were expanded to 0x000E+Y, a new preprocessing number would not be created. The macro expansion proceeds as follows.
4. Preprocessing directives are executed and macro invocations are expanded.
A parameter in the replacement list ... is replaced by the corresponding argument after all macros contained therein have been expanded. Before being substituted, each argument's preprocessing tokens are completely macro replaced as if they formed the rest of the translation unit...Previous Defect Rep8rt < - > Next Defect Report