unterminated unconditional directive error when preprocessing C code

Question

I am having an error in the preprocessing step when compiling a C program.

The odd thing is that I can run the preprocessing with no errors or warnings using:

gcc -I/usr/local/libpng-1.6.24/include -Wall -std=c99 lines.c -E -o lines

but using the form below give me errors:

cpp -I/usr/local/libpng-1.6.24/include -std=c99 lines.c -o lines

I am assuming that cpp is run as part of gcc what makes it more wierd.

For information see below the error I am getting -only one of them, I have many of them of the same sort:

In file included from lines.c:1:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk/usr/include/stdio.h:65:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk/usr/include/Availability.h:172:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk/usr/include/AvailabilityInternal.h:15284:10: error:
    unterminated conditional directive
        #if __MAC_OS_X_VERSION_MIN_REQUIRED >= __MAC_10_11

Needless to notice that the file with the error is a Apple standard file. I must say also that it seems all right to me having all terminating #endif matching their #if directives

Any idea what could be happening here? Or way forward to track down the error?

PS By the way I am running this in OSX with developer tools provided standard by Apple.

--

Adding additional information as a response to some comments:

The source code of lines.c https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-s096-introduction-to-c-and-c-january-iap-2013/final-project/starter-kit/lines.c and to have more context of where the source code is used you might want to see here https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-s096-introduction-to-c-and-c-january-iap-2013/final-project/starter-kit/

If I run gcc without the option -E actually I get a linking problem because of my folder structure but the command below will work with no error -but I do not think this information was relevant for the question because I want to compare like for like and option -E stops after preprocessing and cpp does only preprocessing:

gcc -I/usr/local/libpng-1.6.24/include -L/usr/local/libpng-1.6.24/lib -Wall -std=c99 lines.c -lpng -o lines

--

I have upgraded my Xcode from 7.3 to 8.2.1 and the command line tools from Command_Line_Tools_OS_X_10.11_for_Xcode_7.3 to Command_Line_Tools_macOS_10.12_for_Xcode_8.2 and gcc continues working and cpp still triggering an error. Bu tthis time the error changes a little bit. See below

In file included from lines.c:1:
In file included from /usr/include/stdio.h:65:
In file included from /usr/include/Availability.h:184:
/usr/include/AvailabilityInternal.h:20265:10: error: #else without #if
    #else
/usr/include/AvailabilityInternal.h:20832:10: error: unterminated conditional directive
    #if __MAC_OS_X_VERSION_MIN_REQUIRED >= __MAC_10_11_4

Answer 1

As noted in the comments, I can reproduce your problem on my macOS Sierra 10.12.3 machine with XCode 8, getting (at least) 20 errors so it stops on the 20th.

Source file:

#include <stdio.h>
int main(void) { puts("Hi"); return 0; }

Command line and error output:

$ /usr/bin/cpp -v min.c -o min.c.out >/dev/null
Apple LLVM version 8.0.0 (clang-800.0.42.1)
Target: x86_64-apple-darwin16.4.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
 "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang" -cc1 -triple x86_64-apple-macosx10.12.0 -Wdeprecated-objc-isa-usage -Werror=deprecated-objc-isa-usage -E -disable-free -disable-llvm-verifier -discard-value-names -main-file-name min.c -mrelocation-model pic -pic-level 2 -mthread-model posix -mdisable-fp-elim -masm-verbose -munwind-tables -target-cpu penryn -target-linker-version 274.2 -v -dwarf-column-info -debugger-tuning=lldb -resource-dir /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/clang/8.0.0 -fdebug-compilation-dir /Users/jleffler/soq -ferror-limit 19 -fmessage-length 110 -stack-protector 1 -fblocks -fobjc-runtime=macosx-10.12.0 -fencode-extended-block-signature -fmax-type-align=16 -fdiagnostics-show-option -fcolor-diagnostics -traditional-cpp -o - -x c min.c
clang -cc1 version 8.0.0 (clang-800.0.42.1) default target x86_64-apple-darwin16.4.0
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/clang/8.0.0/include
 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include
 /usr/include
 /System/Library/Frameworks (framework directory)
 /Library/Frameworks (framework directory)
End of search list.
In file included from min.c:1:
In file included from /usr/include/stdio.h:65:
In file included from /usr/include/Availability.h:184:
/usr/include/AvailabilityInternal.h:20265:10: error: #else without #if
        #else
         ^
/usr/include/AvailabilityInternal.h:20832:10: error: unterminated conditional directive
        #if __MAC_OS_X_VERSION_MIN_REQUIRED >= __MAC_10_11_4
         ^
/usr/include/AvailabilityInternal.h:20765:10: error: unterminated conditional directive
        #if __MAC_OS_X_VERSION_MIN_REQUIRED >= __MAC_10_11_3
         ^
/usr/include/AvailabilityInternal.h:20702:10: error: unterminated conditional directive
        #if __MAC_OS_X_VERSION_MIN_REQUIRED >= __MAC_10_11_2
         ^
/usr/include/AvailabilityInternal.h:20643:10: error: unterminated conditional directive
        #if __MAC_OS_X_VERSION_MIN_REQUIRED >= __MAC_10_11
         ^
/usr/include/AvailabilityInternal.h:20588:10: error: unterminated conditional directive
        #if __MAC_OS_X_VERSION_MIN_REQUIRED >= __MAC_10_10_3
         ^
/usr/include/AvailabilityInternal.h:20537:10: error: unterminated conditional directive
        #if __MAC_OS_X_VERSION_MIN_REQUIRED >= __MAC_10_10_2
         ^
/usr/include/AvailabilityInternal.h:20490:10: error: unterminated conditional directive
        #if __MAC_OS_X_VERSION_MIN_REQUIRED >= __MAC_10_10
         ^
/usr/include/AvailabilityInternal.h:20447:10: error: unterminated conditional directive
        #if __MAC_OS_X_VERSION_MIN_REQUIRED >= __MAC_10_9
         ^
/usr/include/AvailabilityInternal.h:20408:10: error: unterminated conditional directive
        #if __MAC_OS_X_VERSION_MIN_REQUIRED >= __MAC_10_8
         ^
/usr/include/AvailabilityInternal.h:20373:10: error: unterminated conditional directive
        #if __MAC_OS_X_VERSION_MIN_REQUIRED >= __MAC_10_7
         ^
/usr/include/AvailabilityInternal.h:20342:10: error: unterminated conditional directive
        #if __MAC_OS_X_VERSION_MIN_REQUIRED >= __MAC_10_6
         ^
/usr/include/AvailabilityInternal.h:20315:10: error: unterminated conditional directive
        #if __MAC_OS_X_VERSION_MIN_REQUIRED >= __MAC_10_5
         ^
/usr/include/AvailabilityInternal.h:20292:10: error: unterminated conditional directive
        #if __MAC_OS_X_VERSION_MIN_REQUIRED >= __MAC_10_4
         ^
/usr/include/AvailabilityInternal.h:20273:10: error: unterminated conditional directive
        #if __MAC_OS_X_VERSION_MIN_REQUIRED >= __MAC_10_3
         ^
In file included from min.c:1:
In file included from /usr/include/stdio.h:65:
/usr/include/Availability.h:233:2: error: #else without #if
#else
 ^
/usr/include/Availability.h:236:2: error: #endif without #if
#endif
 ^
/usr/include/Availability.h:272:2: error: #endif without #if
#endif
 ^
/usr/include/Availability.h:299:2: error: #endif without #if
#endif
 ^
fatal error: too many errors emitted, stopping now [-ferror-limit=]
20 errors generated.
$

Note that the only options I used were -v (to produce the verbose output at the start) and -o min.c.out (which is over-ridden with -o - in the verbose output; it did as it wanted rather than as I told it to do — rank insubordination, really). The redirection of standard output to /dev/null was necessary to avoid seeing all the output, therefore.

If I replace /usr/bin/cpp with /usr/bin/gcc (the path is necessary for me since gcc is /opt/gcc/v6.2.0/bin/gcc, aka GCC 6.2.0), and I add the -E option, it works fine:

$ /usr/bin/gcc -E -v min.c -o min.c.out
Apple LLVM version 8.0.0 (clang-800.0.42.1)
Target: x86_64-apple-darwin16.4.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
 "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang" -cc1 -triple x86_64-apple-macosx10.12.0 -Wdeprecated-objc-isa-usage -Werror=deprecated-objc-isa-usage -E -disable-free -disable-llvm-verifier -discard-value-names -main-file-name min.c -mrelocation-model pic -pic-level 2 -mthread-model posix -mdisable-fp-elim -masm-verbose -munwind-tables -target-cpu penryn -target-linker-version 274.2 -v -dwarf-column-info -debugger-tuning=lldb -resource-dir /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/clang/8.0.0 -fdebug-compilation-dir /Users/jleffler/soq -ferror-limit 19 -fmessage-length 110 -stack-protector 1 -fblocks -fobjc-runtime=macosx-10.12.0 -fencode-extended-block-signature -fmax-type-align=16 -fdiagnostics-show-option -fcolor-diagnostics -o min.c.out -x c min.c
clang -cc1 version 8.0.0 (clang-800.0.42.1) default target x86_64-apple-darwin16.4.0
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/clang/8.0.0/include
 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include
 /usr/include
 /System/Library/Frameworks (framework directory)
 /Library/Frameworks (framework directory)
End of search list.
$ wc -l min.c.out
     456 min.c.out
$

This strongly hints at a problem of some sort in the /usr/bin/cpp program and the way it drives the rest of the compilation tool chain, but I've not identified the crucial difference in the command line.

It also hints at a solution — don't use cpp standalone. As I noted in comments, there was a question from January 2017 — How to get XCode 8 C preprocessor to ignore // comments in #defines? that also pointed to a problem in the standalone cpp.

If you must have a working cpp, then install your own. For example, you could install GCC 6.3.0 (I've been lazy on this machine; my other one is already running 6.3.0, not 6.2.0) in some location (e.g. /opt/gcc/v6.3.0/bin/cpp) and then arrange for that to be run instead of /usr/bin/cpp when you type cpp — adjust PATH, or put a symlink or script in a directory such as /usr/local/bin or $HOME/bin that occurs on PATH before /usr/bin, or specify the correct PATH in the makefile, or whatever it takes.

If you want guidelines on building GCC on a Mac, consider:

• Building GCC on OS X 10.11
• Install GNU GCC on Mac