Don't know what it is. I have checked the headers myself and everything liooks good as far as I can tell.
In file included from /usr/include/SFML/Audio/SoundStream.hpp:31:0,
from /usr/include/SFML/Audio/Music.hpp:31,
from /usr/include/SFML/Audio.hpp:34,
from /home/orm/Engine-CL/theengine/../osound/OSoundCommon.h:18,
from /home/orm/Engine-CL/theengine/../osound/OSound.h:13,
from /home/orm/Engine-CL/theengine/Engine2DCommon.h:16,
from /home/orm/Engine-CL/theengine/Application.h:5,
from /home/orm/Engine-CL/theengine/Application.cpp:1:
/usr/include/SFML/Audio/Sound.hpp:52:10: error: expected identifier before ‘int’
/usr/include/SFML/Audio/Sound.hpp:53:5: error: expected unqualified-id before ‘{’ token
In file included from /usr/include/SFML/Audio/Music.hpp:31:0,
from /usr/include/SFML/Audio.hpp:34,
from /home/orm/Engine-CL/theengine/../osound/OSoundCommon.h:18,
from /home/orm/Engine-CL/theengine/../osound/OSound.h:13,
from /home/orm/Engine-CL/theengine/Engine2DCommon.h:16,
from /home/orm/Engine-CL/theengine/Application.h:5,
from /home/orm/Engine-CL/theengine/Application.cpp:1:
/usr/include/SFML/Audio/SoundStream.hpp:48:18: error: expected unqualified-id before ‘int’
/usr/include/SFML/Audio/SoundStream.hpp:48:18: error: expected ‘;’ before ‘int’
/usr/include/SFML/Audio/SoundStream.hpp:48:18: error: declaration does not declare anything
/usr/include/SFML/Audio/SoundStream.hpp:49:18: error: no members matching ‘sf::Sound::Stopped’ in ‘class sf::Sound’
/usr/include/SFML/Audio/SoundStream.hpp:50:18: error: no members matching ‘sf::Sound::Paused’ in ‘class sf::Sound’
/usr/include/SFML/Audio/SoundStream.hpp:51:18: error: no members matching ‘sf::Sound::Playing’ in ‘class sf::Sound’
make[2]: *** [CMakeFiles/Engine2D.dir/theengine/Application.o] Error 1
make[1]: *** [CMakeFiles/Engine2D.dir/all] Error 2
make: *** [all] Error 2
I am using the current package available in the ArchLinux repositories and am linking with sfml-system and sfml-audio in that order.