continued lines not always merged into one long line

[J. Lewis Muir]

The GCC C preprocessor sometimes incorrectly handles a line continuation by not joining a following line with the current line.

Attached is a simple C file called continued-line-test.c. It contains the following three lines (the first two lines end with a backslash):

struct {\
  int x;\
};

Running gcc with the -E option produces the following:

$ gcc -E continued-line-test.c
# 1 "continued-line-test.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "continued-line-test.c"
struct {
  int x;};

As you can see, even though the first line in continued-line-test.c ended with a backslash, the second line was not joined with the first line. Of course, this is a simple example, but I have software that depends on correct line continuation processing in order to build.

The GCC documentation (http://gcc.gnu.org/onlinedocs/gcc-4.6.3/cpp/Initial-processing.html#Initial-processing) says:

"A continued line is a line which ends with a backslash, `\'. The backslash is removed and the following line is joined with the current one. No space is inserted, so you may split a line anywhere, even in the middle of a word. (It is generally more readable to split lines only at white space.)"

The observed behavior is inconsistent with this statement from the documentation.

What I expected to see is the following:

$ gcc -E continued-line-test.c
# 1 "continued-line-test.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "continued-line-test.c"
struct { int x;};

Here's my Ubuntu version information:

$ lsb_release -rd
Description: Ubuntu 12.04.1 LTS
Release: 12.04

And here's the package version information:

$ apt-cache policy gcc-4.6
gcc-4.6:
  Installed: 4.6.3-1ubuntu5
  Candidate: 4.6.3-1ubuntu5
  Version table:
 *** 4.6.3-1ubuntu5 0
        500 http://us.archive.ubuntu.com/ubuntu/ precise/main i386 Packages
        100 /var/lib/dpkg/status

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: gcc 4:4.6.3-1ubuntu5
ProcVersionSignature: Ubuntu 3.2.0-32.51-generic 3.2.30
Uname: Linux 3.2.0-32-generic i686
NonfreeKernelModules: prl_fs_freeze prl_fs prl_tg prl_eth
ApportVersion: 2.0.1-0ubuntu14
Architecture: i386
Date: Mon Nov 5 10:29:32 2012
InstallationMedia: Ubuntu 10.04.1 LTS "Lucid Lynx" - Release i386 (20100816.1)
ProcEnviron:
 TERM=xterm
 PATH=(custom, user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: gcc-defaults
UpgradeStatus: Upgraded to precise on 2012-05-03 (186 days ago)

[J. Lewis Muir (jlmuir)]

I'm also able to reproduce this problem in GCC 4.7.2. I've submitted a bug report to the GCC project (bug #55242). It can be viewed at <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55242>.

[J. Lewis Muir (jlmuir)]

According to the comment made at 2012-11-09 20:23:47 UTC by Dmitry Gorbachev on the GCC bug report, this behavior is a feature, not a bug. So, sorry for the trouble; this Ubuntu bug report can be closed.