* Is -fcommon reliable?
@ 2018-03-16 16:56 Robert Henderson
0 siblings, 0 replies; only message in thread
From: Robert Henderson @ 2018-03-16 16:56 UTC (permalink / raw)
To: gcc-help
Hi,
Consider the the following code:
// Header foo.h:
const double FooLength;
const double FooMass;
// Source file foo.c:
#include "foo.h"
const double FooLength = 4.2;
const double FooMass = 10.5;
// Source file bar.c:
#include foo.h
...
This is non-standard C, but it is correct if you rely on the '-fcommon'
feature of GCC which merges tentative definitions across translation
units. I find '-fcommon' to be a convenient and useful feature because
it allows you to omit 'extern' specifiers on declarations of global
constants.
My question is: if I rely on '-fcommon' in this way in my own software,
is it likely to cause any problems for me down the line? For example,
are there any plans to deprecate '-fcommon' in GCC in the future?
Regards,
Rob Henderson
Additional notes:
() The '-fcommon' functionality is described in K&R in a footnote (2nd
edition, Sect. A10.2, pg. 227) as an "alternate formulation, ... usual
in UNIX systems and recognised as a common extension by the Standard".
() The GNU LD manual, Sect. 2.1, describes reliance on '-fcommon' as a
"somewhat sloppy practice".
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