Use of Macro for static declaration

Question

While reviewing C code that has been migrated from AIX to Cygwin 64-bit, I came across the following snippet. Writing only "static" within the "#ifndef" directive doesn't make sense to me. Since no documentation or help was available, I am asking for help here to understand the meaning of this code. Could someone explain if the code is valid and, if so, why? It appears to compile and run, but what effect will "static" have here?

#ifndef __CYGWIN__
#define __CYGWIN__

static const char ccm_version[] = "%%%CCM_VERSION: %full_filespec: %%%"; /*#006#*/

#ifdef __CYGWIN__
static
#endif
void somefunc(void);
void somefunc(void) { 
    printf("%s \n", ccm_version); 
} /*#006#*/

I am using Cygwin 64 bit on Windows 11 Pro and gcc (GCC) 11.3.0

Answer 1

It is valid and in case __CYGWIN__ is defined, the code applies static to the function prototype: static void somefunc(void);. So it's equivalent to this:

#ifdef __CYGWIN__
  static void somefunc(void);
#else
  void somefunc(void);
#endif

Having a function declaration immediately followed by the corresponding function definition is rather pointless... they could as well have applied the static storage specifier directly to the function definition.

As for what that's supposed to be good for here, I can't say for sure without some context. Making a function static will give it internal linkage and limit access from other translation units. Reasons for doing so could be private encapsulation, resolving multiple identifier linker problems, doing some local unit testing, encouraging function inlining etc etc. Why it was used here, I can't tell, though encouraging inlining during code generation seems likely.