Strange, I download sdk sfml and I try to compile it with make :
g++ -o Image.o -c Image.cpp -W -Wall -pedantic -I../../../include -I../../ -O2 -DNDEBUG -fPIC -I/usr/include/freetype2
In file included from ../../../include/SFML/System/Resource.hpp:211:0,
from ../../../include/SFML/Graphics/Image.hpp:31,
from Image.cpp:28:
../../../include/SFML/System/ResourcePtr.inl: In constructor ‘sf::ResourcePtr< <template-parameter-1-1> >::ResourcePtr()’:
../../../include/SFML/System/ResourcePtr.inl:31:12: error: ‘NULL’ was not declared in this scope
In file included from ../../../include/SFML/System/Resource.hpp:211:0,
from ../../../include/SFML/Graphics/Image.hpp:31,
from Image.cpp:28:
../../../include/SFML/System/ResourcePtr.inl: In member function ‘void sf::ResourcePtr< <template-parameter-1-1> >::OnResourceDestroyed()’:
../../../include/SFML/System/ResourcePtr.inl:148:18: error: ‘NULL’ was not declared in this scope
make[2]: *** [Image.o] Error 1
make[2]: Leaving directory `/home/alexandre/Downloads/SFML-1.6/src/SFML/Graphics'
make[1]: *** [sfml-graphics] Error 2
make[1]: Leaving directory `/home/alexandre/Downloads/SFML-1.6/src/SFML'
make: *** [sfml] Error 2