[FFmpeg-devel] [PATCH v3 1/1] configure: Refactor setting of feature test macro _XOPEN_SOURCE

[Jörg Krause]

Some C libraries, eg glibc, uclibc, and musl, uses feature test macros 
to expose definitions conforming to the standards ISO C, POSIX and 
extensions. According to which feature test macros are defined by the 
user or the compiler, a header file, eg <features.h>, used by these 
libraries internally defines various other macros.

glibc and uclibc also defines release test macros, eg __GLIBC__ and
__UCLIBC__ in <features.h>. musl does not have (and does not want) a 
macro __MUSL__. Therefore it is not possible to check for the musl
library.

However, building FFmpeg with musl needs the feature test macro
_XOPEN_SOURCE=600 to be defined.

Signed-off-by: Jörg Krause <jkrause at posteo.de>
---
Changes v2 -> v3:
  - set _XOPEN_SOURCE as default in case no C library can be detected

Changes v1 -> v2:
  - do not set _XOPEN_SOURCE twice for glibc and uclibc
---
 configure | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/configure b/configure
index 110a3fd..b9707c5 100755
--- a/configure
+++ b/configure
@@ -4229,6 +4229,9 @@ probe_libc(){
     elif check_${pfx}cpp_condition sys/brand.h "defined LABELED_BRAND_NAME"; then
         eval ${pfx}libc_type=solaris
         add_${pfx}cppflags -D__EXTENSIONS__ -D_XOPEN_SOURCE=600
+    # FFmpeg needs a POSIX.1-2001/XSI compliant C library
+    else
+        add_${pfx}cppflags -D_XOPEN_SOURCE=600
     fi
 }
 
-- 
2.1.0