[oi-dev] feature.h and __XOPEN_SOURCE_EXTENDED

Alexander Pyhalov alp at rsu.ru
Thu Jun 6 09:15:48 UTC 2013

Ok, while building ncurses I encountered the following problem.

It seems that a lot of projects define __XOPEN_SOURCE_EXTENDED macros.
When it is tested in feature_tests.h the value of __XOPEN_SOURCE is 
ignored, and we have problems - _XPG5 is not defined for gcc 3.4 and 
_XPG5 and _XPG6 are not defined for gcc4.7.
So, we miss some declarations in wchar.h/wchar_iso.h
for example because of  the following macro
#if (!defined(_XPG4) && !defined(_XPG4_2) || defined(_XPG5))

and possibly receive the following error with gcc 4.7 from feature_test.h:

if defined(_STDC_C99) && (defined(__XOPEN_OR_POSIX) && !defined(_XPG6))
#error "Compiler or options invalid for pre-UNIX 03 X/Open applications \
         and pre-2001 POSIX applications"

It seems the following patch solves the problem.
Is it a correct solution or I just don't see potential problems?
Or, alternavely we could add && (_XOPEN_SOURCE - 0 < 500) condition to

#elif (defined(_XOPEN_SOURCE) && _XOPEN_SOURCE_EXTENDED - 0 == 1)

This condition is used in the first #if branch.

2013-05-29 16:15:49.497379177 +0400
+++ /usr/include/sys/feature_tests.h    2013-06-06 12:57:43.994292322 +0400
@@ -275,8 +275,9 @@
  #define        _XPG4_2
  #define        _XPG4
  #define        _XPG3
  /* X/Open CAE Specification, Issue 5 */
-#elif  (_XOPEN_SOURCE - 0 == 500)
+#if    (_XOPEN_SOURCE - 0 == 500)
  #define        _XPG5
  #define        _XPG4_2
  #define        _XPG4

Best regards,
Alexander Pyhalov,
system administrator of Computer Center of Southern Federal University

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