Re: Mac Build Error

[David Morsberger <dave () morsberger com>]

On Thu, Jan 21, 2016 at 2:29 PM, Guy Harris <guy () alum mit edu> wrote:

> On Jan 21, 2016, at 6:08 AM, David Morsberger <dave () morsberger com> wrote:
>
> > It appears the linker isn’t called when the -c and the -o options are
> present.
>
> Correct.  It's not *supposed* to be called.  In UNIX C compilers, the "-c"
> flag means "compile to an object file, but don't link the resulting object
> file into an executable file"; it's the standard option used if you have a
> program that's built from more than one object file.
>
> > The cmake logic in CMakeLists.txt is basically:
> >
> >    SET(CMAKE_REQUIRED_FLAGS "${_FLAG}")
> >    CHECK_C_SOURCE_RUNS(“int main() { return 0;}" ${_RESULT})
>
> The documentation for the CHECK_C_SOURCE_RUNS() macro is
>
>         * CheckCSourceRuns: Check if the given C source code compiles and
> runs.
I think this is a bug in cmake because:

1. the 'and run' in "CheckCSourceRuns: Check if the given C source code
compiles and runs" should imply linking and executing the software.

2. The CHECK_C_SOURCE_COMPILES should only try and compile source

There is no other way to test that a program links since the '-c <file.c>
and -o <file.o>' options result in only compiling.


> I guess, with Makefiles, the linking is done with a compiler command
> (another UNIX tradition) and the -Wl,--as-needed flag is passed on the link
> command line, but, with Xcode, it's not done with a compiler command, and
> the C flags aren't passed to the link phase at all.
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