对‘google::FlagRegisterer::FlagRegisterer＜unsigned long＞(char const*, char const*, )’未定义的引用

问题分析：应该是没有正确引入gflags

解决方法：
1.安装gflags

git clone https://github.com/gflags/gflags.git`

cd gflags

mkdir build

cd build

cmake ..

make

sudo make install

2.在相应的CMakeLists.txt中添加

find_package(gflags REQUIRED) 

target_link_libraries(gflags)