🚀 go-pugleaf

In article <ntvfii4@fido.asd.sgi.com> shankar@sgi.com (Shankar Unni) writes:
|
|What is the accepted opinion as to the legality of a "#if" and a
|"#else" or "#endif" being in different files, as in:
|
| a.c:
|
|    #ifdef __STDC__
|    #include "a.h"
|
| a.h:
|
|    main() { }
|    #endif /* __STDC__ */
|
|
|Should the above compile? Not compile? Implementation-defined?

It shouldn't compile. Have a look at the syntax of a preprocessing-file:
ANSI 3.8 Preprocessing directives:

preprocessing-file:
	group_opt

group:
	group-part
	...

group-part:
	if-section
	control-line
	...

if-section:
	if-group elif-groups_opt else-group_opt endif-line

control-line:
	#include pp-tokens new-line
	...

As you can see, the entire #if ... #endif structure has to be present
in _one_ preprocessing file. The #include control line has to be processed
recursively as stated in ANSI 2.1.1.2 Translation phases:

`A #include preprocessing directive causes the named header or source file
 to be processed from phase 1 through phase 4 recursively.'

A footnote states:

`Implementations must behave as if these separate phaases occur, even
 though many are typically folded together in practice.'

So an #include directive is a bit more than just a switch from one
file to another for the lexical analyzer (after stacking the previous
file descriptors of course.)

kind regards,

Jos aka jos@and.nl