In file included from /usr/include/c++/4.4/unordered_map:35, from entries.cpp:3: /usr/include/c++/4.4/c++0x_warning.h:31:2: error: #error This file requires compiler and library support for the upcoming ISO C++ standard, C++0x. This support is currently experimental, and must be enabled with the -std=c++0x or -std=gnu++0x compiler options. entries.cpp:8: error: expected constructor, destructor, or type conversion before '<' token entries.cpp: In function 'int main()': entries.cpp:27: error: 'M' was not declared in this scope entries.cpp:28: error: 'M' was not declared in this scope entries.cpp:29: error: 'M' was not declared in this scope