This issue has been automatically converted from the original issue lists and some formatting may not have been preserved.
Authors: Kuo-Wei Lee, WG14
Date: 1992-12-10
Reference document: X3J11/91-046
Submitted against: C90
Status: Closed
Converted from: dr.htm, dr_038.html
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)?
Comment from WG14 on 1997-09-23:
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)...
4. Preprocessing directives are executed and macro invocations are expanded.
Therefore, if X+Y were expanded to 0x000E+Y, a new preprocessing number
would not be created. The macro expansion proceeds as follows.
FOO(X+Y) (6 tokens) --
FOO(0x000E+0x0100) (6 tokens) --
0x000E+0x0100 (3 tokens)
This sequence is required by subclause 6.8.3.1, page 90, lines 10-14:
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...