dlib 示例，测试构建失败
dlib example, test builds fail
运行 ubuntu 12.04，我下载源码按照说明编译（见https://github.com/davisking/dlib）。以下是显示的错误消息。
cmake --build . --config Release
[ 1%] Building CXX object dlib_build/CMakeFiles/dlib.dir/bsp/bsp.cpp.o
In file included from /home/andreif/downlib/dlib-19.2/dlib/bsp/../sockets/../threads/parallel_for_extension.h:9:0,
from /home/my_path/dlib-19.2/dlib/bsp/../sockets/../threads.h:24,
from /home/my_path/dlib-19.2/dlib/bsp/../sockets/sockets_kernel_2.h:33,
from /home/my_path/dlib-19.2/dlib/bsp/../sockets/posix.h:4,
from /home/my_path/dlib-19.2/dlib/bsp/../sockets.h:14,
from /home/my_path/dlib-19.2/dlib/bsp/bsp.h:7,
from /home/my_path/dlib-19.2/dlib/bsp/bsp.cpp:6:
/home/my_path/dlib-19.2/dlib/bsp/../sockets/../threads/async.h: In function ‘std::future<typename std::result_of<_Functor(_ArgTypes="" ...)="">::type> dlib::async(dlib::thread_pool&, Function&&, Args&& ...)’:
/home/my_path/dlib-19.2/dlib/bsp/../sockets/../threads/async.h:63:15: error: expected nested-name-specifier before ‘bind_t’
/home/my_path/dlib-19.2/dlib/bsp/../sockets/../threads/async.h:63:15: error: ‘bind_t’ has not been declared
/home/my_path/dlib-19.2/dlib/bsp/../sockets/../threads/async.h:63:22: error: expected ‘;’ before ‘=’ token
/home/my_path/dlib-19.2/dlib/bsp/../sockets/../threads/async.h:63:22: error: expected primary-expression before ‘=’ token
/home/my_path/dlib-19.2/dlib/bsp/../sockets/../threads/async.h:63:24: error: expected primary-expression before ‘decltype’
/home/my_path/dlib-19.2/dlib/bsp/../sockets/../threads/async.h:63:24: error: expected ‘;’ before ‘decltype’
/home/my_path/dlib-19.2/dlib/bsp/../sockets/../threads/async.h:64:37: error: ‘bind_t’ was not declared in this scope
make[2]: [dlib_build/CMakeFiles/dlib.dir/bsp/bsp.cpp.o] Error 1
make[1]: [dlib_build/CMakeFiles/dlib.dir/all] Error 2
make: *** [all] Error 2
问题是我的 c++ 编译器：ubuntu 12.04 中的默认 gcc 4.6 支持 c++11，但调用它时必须在命令行中启用它。我尝试编辑 /.bashrc 以自动执行此操作，但没有成功。我的解决方案是安装 gcc/g++ 4.8（并使用 update-alternatives 来保持旧安装可用），如此处所述
http://mortenvp.com/installing-a-newer-gccg-on-ubuntu-12-04-lts/
运行 ubuntu 12.04，我下载源码按照说明编译（见https://github.com/davisking/dlib）。以下是显示的错误消息。
cmake --build . --config Release
[ 1%] Building CXX object dlib_build/CMakeFiles/dlib.dir/bsp/bsp.cpp.o
In file included from /home/andreif/downlib/dlib-19.2/dlib/bsp/../sockets/../threads/parallel_for_extension.h:9:0,
from /home/my_path/dlib-19.2/dlib/bsp/../sockets/../threads.h:24,
from /home/my_path/dlib-19.2/dlib/bsp/../sockets/sockets_kernel_2.h:33,
from /home/my_path/dlib-19.2/dlib/bsp/../sockets/posix.h:4,
from /home/my_path/dlib-19.2/dlib/bsp/../sockets.h:14,
from /home/my_path/dlib-19.2/dlib/bsp/bsp.h:7,
from /home/my_path/dlib-19.2/dlib/bsp/bsp.cpp:6:
/home/my_path/dlib-19.2/dlib/bsp/../sockets/../threads/async.h: In function ‘std::future<typename std::result_of<_Functor(_ArgTypes="" ...)="">::type> dlib::async(dlib::thread_pool&, Function&&, Args&& ...)’:
/home/my_path/dlib-19.2/dlib/bsp/../sockets/../threads/async.h:63:15: error: expected nested-name-specifier before ‘bind_t’
/home/my_path/dlib-19.2/dlib/bsp/../sockets/../threads/async.h:63:15: error: ‘bind_t’ has not been declared
/home/my_path/dlib-19.2/dlib/bsp/../sockets/../threads/async.h:63:22: error: expected ‘;’ before ‘=’ token
/home/my_path/dlib-19.2/dlib/bsp/../sockets/../threads/async.h:63:22: error: expected primary-expression before ‘=’ token
/home/my_path/dlib-19.2/dlib/bsp/../sockets/../threads/async.h:63:24: error: expected primary-expression before ‘decltype’
/home/my_path/dlib-19.2/dlib/bsp/../sockets/../threads/async.h:63:24: error: expected ‘;’ before ‘decltype’
/home/my_path/dlib-19.2/dlib/bsp/../sockets/../threads/async.h:64:37: error: ‘bind_t’ was not declared in this scope
make[2]: [dlib_build/CMakeFiles/dlib.dir/bsp/bsp.cpp.o] Error 1
make[1]: [dlib_build/CMakeFiles/dlib.dir/all] Error 2
make: *** [all] Error 2
问题是我的 c++ 编译器：ubuntu 12.04 中的默认 gcc 4.6 支持 c++11，但调用它时必须在命令行中启用它。我尝试编辑 /.bashrc 以自动执行此操作，但没有成功。我的解决方案是安装 gcc/g++ 4.8（并使用 update-alternatives 来保持旧安装可用），如此处所述
http://mortenvp.com/installing-a-newer-gccg-on-ubuntu-12-04-lts/