backslash whitespace newline

[Howard Hinnant]

I've been reviewing the age-old issue of interpreting  
<whitespace>*<newline> as the end-of-line indicator as is the current  
practice with gcc.  For those not familiar with this issue, gcc takes  
advantage of C99's 5.1.1.2p1b1 "implementation-defined manner" to  
convert multibyte end-of-line indicators to newline characters.  gcc  
considers zero or more whitespace characters preceding a more  
traditional CR and/or LF as the end-of-line indicator.  This behavior  
can cause differences in some code compared to compilers which do not  
strip trailing whitespace off of lines.  For example:

// comment \
int x;
int y;

Pretend there's one or more spaces or tabs after the '\'.  gcc will  
interpret this as:

A:

// comment int x;
int y;

while other compilers (Microsoft, EDG-based, CodeWarrior to name a  
few) interpret it as:

B:

// comment
int x;
int y;

And depending on what you're trying to do, either A or B is the  
"correct" answer.  I've seen code broken either way (by assuming A  
and having the compiler do B and vice-versa).

This issue has recently been discussed on the C standards reflector,  
and though I was not privy to that discussion, my understanding is  
that the likely resolution from this standards body will be that a  
compiler implementing either A or B is conforming.

That being said, gcc to the best of knowledge, is the only modern  
compiler to implement end-of-line whitespace stripping (yes I'm aware  
of older compilers and dealing with punch cards). So on the basis of  
conforming to a de-facto standard alone, I propose that gcc abandon  
end-of-line whitespace stripping, or at least strip 2 or more  
whitespace characters down to 1 space instead of to 0 spaces during  
translation phase 1.

I realize that this change could break some existing code.  But I am  
also aware of existing code wishing to port to gcc which is broken by  
gcc's current behavior.  If we want gcc to "gain market share", does  
it not make sense to "welcome" new comers when possible by adopting  
what is otherwise industry-wide practice?

Thanks,
Howard