error 'sort' was not declared in this scope

[epicTCK]

g++ -std=c++11   -c -o main.o main.cpp
g++ -std=c++11   -c -o any-ticker.o any-ticker.cpp
g++ -std=c++11   -c -o typeset.o typeset.cpp
g++ -std=c++11   -c -o set_parameters.o set_parameters.cpp
g++ -std=c++11   -c -o file_convert.o file_convert.cpp
g++ -std=c++11   -c -o rleto106.o rleto106.cpp
g++ -std=c++11   -c -o life_object.o life_object.cpp
life_object.cpp: In static member function ‘static void LifeObject::write()’:
life_object.cpp:74:43: error: ‘sort’ was not declared in this scope
  sort(outputDots.begin(), outputDots.end());
                                           ^
make: *** [life_object.o] Error 1