extern const initialized warns in C

[Jay K <jayk123 at hotmail dot com>]

extern const int foo = 123;



Why does this warn?
This is a valid portable form, with the same meaning
across all compilers, and, importantly, portably
to C and C++.

I explicitly do not want to say:

  const int foo = 123

because I want the code to be valid and have the same meaning
in C and C++ (modulo name mangling).

I end up with:

// Workaround gcc warning.
#ifdef __cplusplus
#define EXTERN_CONST extern const
#else
#define EXTERN_CONST const
#endif


EXTERN_CONST int foo = 123;

and having to explain it to people.

$ cat 1.c
extern const int foo = 123;
$ $HOME/gcc720/bin/gcc -c -S 1.c
1.c:1:18: warning: 'foo' initialized and declared 'extern'
 extern const int foo = 123;
                  ^~~
$ $HOME/gcc720/bin/gcc -c -S -xc++ -Wall -pedantic 1$ $HOME/gcc720/bin/gcc -v
Using built-in specs.

COLLECT_GCC=/Users/jay/gcc720/bin/gcc
COLLECT_LTO_WRAPPER=/Users/jay/gcc720/libexec/gcc/x86_64-apple-darwin16.7.0/7.2.0/lto-wrapper
Target: x86_64-apple-darwin16.7.0
Configured with: ../gcc-7.2.0/configure -prefix=/Users/jay/gcc720 -disable-nls -disable-bootstrap
Thread model: posix
gcc version 7.2.0 (GCC) $ 


Thank you,
 - Jay