Re: lily/freetype-error.cc: const struct #include ;

[Werner LEMBERG]

>> As a C programmer, it took me about 30 seconds (or less) to twig what it
>> was doing.
> 
> Could you take 120 seconds or so to explain what it's doing?  I'm
> supposed to be teaching first-year C programming, and I haven't run
> across this before.

Here is the documentation from fterrors.h:

  /*************************************************************************/
  /*                                                                       */
  /* This special header file is used to define the handling of FT2        */
  /* enumeration constants.  It can also be used to generate error message */
  /* strings with a small macro trick explained below.  [...]              */
  /*                                                                       */
  /* II - Error Message strings                                            */
  /* --------------------------                                            */
  /*                                                                       */
  /*   The error definitions below are made through special macros that    */
  /*   allow client applications to build a table of error message strings */
  /*   if they need it.  The strings are not included in a normal build of */
  /*   FreeType 2 to save space (most client applications do not use       */
  /*   them).                                                              */
  /*                                                                       */
  /*   To do so, you have to define the following macros before including  */
  /*   this file:                                                          */
  /*                                                                       */
  /*   FT_ERROR_START_LIST ::                                              */
  /*     This macro is called before anything else to define the start of  */
  /*     the error list.  It is followed by several FT_ERROR_DEF calls     */
  /*     (see below).                                                      */
  /*                                                                       */
  /*   FT_ERROR_DEF( e, v, s ) ::                                          */
  /*     This macro is called to define one single error.                  */
  /*     `e' is the error code identifier (e.g. FT_Err_Invalid_Argument).  */
  /*     `v' is the error numerical value.                                 */
  /*     `s' is the corresponding error string.                            */
  /*                                                                       */
  /*   FT_ERROR_END_LIST ::                                                */
  /*     This macro ends the list.                                         */
  /*                                                                       */
  /*   Additionally, you have to undefine __FTERRORS_H__ before #including */
  /*   this file.                                                          */
  /*                                                                       */
  /*   Here is a simple example:                                           */
  /*                                                                       */
  /*     {                                                                 */
  /*       #undef __FTERRORS_H__                                           */
  /*       #define FT_ERRORDEF( e, v, s )  { e, s },                       */
  /*       #define FT_ERROR_START_LIST     {                               */
  /*       #define FT_ERROR_END_LIST       { 0, 0 } };                     */
  /*                                                                       */
  /*       const struct                                                    */
  /*       {                                                               */
  /*         int          err_code;                                        */
  /*         const char*  err_msg;                                         */
  /*       } ft_errors[] =                                                 */
  /*                                                                       */
  /*       #include FT_ERRORS_H                                            */
  /*     }                                                                 */
  /*                                                                       */
  /*************************************************************************/

fterrors.h defines fallbacks for those macros, and lilypond simply
uses them.

> But why does the #include need to be in the middle of the = and ; ?

I hope that the explanation above gives you the idea.


    Werner