Causing cpp (C preprocessor) to remove C++ comments on Mac OS X

I have a user report (unfortunately can't verify it due to lack of appropriate machine) that the C preprocessor (cpp) command on Mac OS X 10.6.4 doesn't remove C++/C99 double slash // comments from files it processes,开发者_StackOverflow社区 no matter what option it's given. This is the gcc version:

 i686-apple-darwin10-gcc-4.2.1 (GCC) 4.2.1 (Apple Inc. build 5664)

Is it possible to somehow cause it to remove such comments, as one would expect from a C++ preprocessor (this is needed because cpp is used as part of another tool).

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I've found a formula that works with the cpp command: try cpp -xc++ (note the lack of spaces between -x and c++).

$ printf '/* block comment */\n// line comment\nnot a comment\n' | cpp -xc++
# 1 "<stdin>"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "<stdin>"


not a comment

contrast:

$ printf '/* block comment */\n// line comment\nnot a comment\n' | cpp -x c++
i686-apple-darwin10-gcc-4.2.1: c: No such file or directory
i686-apple-darwin10-gcc-4.2.1: c++: No such file or directory
i686-apple-darwin10-gcc-4.2.1: warning: '-x -x' after last input file has no effect
i686-apple-darwin10-gcc-4.2.1: no input files

Now '-x c++' is SUPPOSED to work, and DOES work on my Linux box (with gcc 4.4, but I recall it working as long ago as gcc 2.95) so it seems that Apple broke it.

I really must reemphasize the importance of providing a complete, precise test case for questions like these. It did not occur to me yesterday to look for Apple having introduced a bug, because I know that wilx's answer should have worked, and in the absence of a precise description of what the OP's user tried, it was far more likely that they had something else on their actual command line that was negating it. If the command line and error messages I show above were provided in the original question, that would have targeted everyone's attention much more effectively.

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Try adding either -x c++ or -x c -std=c99 to the command line.

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One partial solution that appears to work is invoke gcc -E instead of cpp.

 -E                       Preprocess only; do not compile, assemble or link

This indeed strips // comments on Mac OS X.

However, I'm still curious why there are problems with cpp itself.