Problem with c2hs on Mac OS Leopard about c2hs HOT 1 CLOSED

Original comment date: 2008-07-15T22:03:51-0700

I believe this is a problem with CPP and nested conditionals on Leopard. Using OSX 10.5.2, with

cpp --version
i686-apple-darwin9-gcc-4.0.1 (GCC) 4.0.1 (Apple Inc. build 5465)

running cpp (not c2hs) on this text

#if 1
    #if 1
        int foo1();
    #else
        int foo2();
    #endif
#else
    int bar();
#endif

yields this result:

# 1 "foo2.chs"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "foo2.chs"

    #if 1
        int foo1();
    #else
        int foo2();
    #endif

using #ifdef instead of #if seems to make no difference.

I don't know yet if this is fixed in 10.5.4, or by installing a newer gcc.

cpp (gcc-4.0.1 on leopard) doesn't process indented preprocessor directives. Maybe there's a flag for cpp which circumvents this problem, I don't know.

As the documentation (man page) of cpp seems to be out-of-date too, I'd suggest to use ghc -E instead.

That is, invoke c2hs this way

c2hs -c ghc -C -E ...

Here's a small example once again documenting the problem:

$ cat test.h
#ifdef FOO
#endif
  #ifdef FOO
  #endif
$ cpp test.h
# 1 "test.h"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "test.h"


  #ifdef FOO
  #endif
$ gcc -E test.h
# 1 "test.h"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "test.h"

best regards, benedikt

I'm sorry, this should read:

...

I'd suggest to use gcc -E instead.

That is, invoke c2hs this way

c2hs -c gcc -C -E ...

...

This should actually work:

c2hs -c gcc -C "-E -x c" ... 

This causes c2hs to execute

gcc  -x=c -E -x c

such that -x c (use C as language) overrides the invalid -x=c flag.

The long story:

On Mac Os X (10.5), cpp is a shell script supplied for backwards compatiblity:

$ head -n 11 /usr/bin/cpp 
#!/bin/sh
#
# Transitional front end to CCCP to make it behave like (Reiser) CCP:
#   specifies -traditional
#   doesn't search gcc-include
#
# Please beware that this program exists only to provide legacy BSD
#    software access to cccp. Direct access to the C pre-processor
#    is deprecated; it is only supported for use by the cc(1) C
#    compiler. Use of cccp for anything other than C code is a bad
#    idea. Don't do it. If you want a macro processor, use m4(1).

-traditional implies that preprocessor directives have to start at the first column of a file.

When invoking cpp on Mac Os X, you're /roughly/ executing

gcc -E -traditional -x c ...

Therefore, one should use ghc -E on darwin9 instead of cpp, and if we need to use cpp, one shouldn't pass -x=c to the preprocessor.

benedikt

Patch to use gcc -E instead of cpp on darwin

Now using gcc -E on darwin. Probably should use it everywhere.

from c2hs.