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 3.2 Function-like Macros
 ========================
 
 You can also define macros whose use looks like a function call.  These
 are called "function-like macros".  To define a function-like macro,
 you use the same `#define' directive, but you put a pair of parentheses
 immediately after the macro name.  For example,
 
      #define lang_init()  c_init()
      lang_init()
           ==> c_init()
 
    A function-like macro is only expanded if its name appears with a
 pair of parentheses after it.  If you write just the name, it is left
 alone.  This can be useful when you have a function and a macro of the
 same name, and you wish to use the function sometimes.
 
      extern void foo(void);
      #define foo() /* optimized inline version */
      ...
        foo();
        funcptr = foo;
 
    Here the call to `foo()' will use the macro, but the function
 pointer will get the address of the real function.  If the macro were to
 be expanded, it would cause a syntax error.
 
    If you put spaces between the macro name and the parentheses in the
 macro definition, that does not define a function-like macro, it defines
 an object-like macro whose expansion happens to begin with a pair of
 parentheses.
 
      #define lang_init ()    c_init()
      lang_init()
           ==> () c_init()()
 
    The first two pairs of parentheses in this expansion come from the
 macro.  The third is the pair that was originally after the macro
 invocation.  Since `lang_init' is an object-like macro, it does not
 consume those parentheses.
 

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