ubuntu下编译、安装及使用gflags

The gflags package contains a C++ library that implements commandline flags processing. It includes built-in support for standard types such as string and the ability to define flags in the source file in which they are used.

https://zhuanlan.zhihu.com/p/108477489

gflags是什么？

gflags是google开源的命令行标记处理库；
那么什么是命令行标记呢？顾名思义就是当运行一个可执行文件时，由用户为其指定的标记，形如：

 fgrep -l -f ./test ccc jjj

注意上述命令，-l与-f ./test是命令行标记，而ccc与jjj是命令行参数，因为这两者不是以破折号开头的。一般的一个可执行文件，允许用户为其传入命令行标记以及参数，如上述例子，-l是一个不带参数的标记，-f是一个带了参数“./test”的标记，而gflags可以解析这些标记以及参数并将其存储在某些数据结构中。

https://blog.csdn.net/qq_22634949/article/details/101718879

1，安装gflags

git clone https://github.com/gflags/gflags.git
cd gflags
mkdir build && cd build
cmake .. -DGFLAGS_NAMESPACE=google -DCMAKE_CXX_FLAGS=-fPIC ..
make -j4
sudo make install

注意，如在后期make时遇到错误something wrong with flag 'flagfile' in file 'XXX.cc'，eg，something wrong with flag 'logtostderr' in file '/root/glog/src/logging.cc'， you are possibly trying to link file XXX.cc both statically and dynamically into the executable。因此，除静态链接库以外，还需要build一个动态链接库。使用cmake时，将BUILD_SHARED_LIBS设置为ON，并重新编译gflags。如下

git clone https://github.com/gflags/gflags.git
cd gflags
mkdir build && cd build
cmake -DGFLAGS_NAMESPACE=google -DCMAKE_CXX_FLAGS=-fPIC -DBUILD_SHARED_LIBS=ON ..
make -j4
sudo make install
sudo ldconfig

最后一句sudo ldconfig，加载动态链接库，一般是编译安装软件时候出现动态链接库报错需要手动加载。

2，gflags的使用

https://blog.csdn.net/qq_39451578/article/details/115679961?utm_medium=distribute.pc_relevant.none-task-blog-baidujs_title-0&spm=1001.2101.3001.4242

• 文件

main.cpp

#include 
#include 
#include 
#include 

DEFINE_bool(isvip, false, "If Is VIP");
DEFINE_string(ip, "127.0.0.1", "connect ip");
DECLARE_int32(port);
DEFINE_int32(port, 80, "listen port");
// DECLARE_double(test);
DEFINE_double(test, 0.01, "ddd");

int main(int argc, char** argv)
{
  // gflag使用：
  google::ParseCommandLineFlags(&argc, &argv, true);
  std::cout<<"test:"<

CMakeLists.txt

cmake_minimum_required(VERSION 2.8.12)
project(mout)
 
# set(CMAKE_BUILD_TYPE "Debug") # Debug/Release
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
# set(EXECUTABLE_OUTPUT_PATH ${PROJECT_SOURCE_DIR}/bin)
 
find_package(gflags REQUIRED)
include_directories(${GFLAGS_INCLUDE_DIR})
find_package(glog REQUIRED)
include_directories(${GLOG_INCLUDE_DIRS})
 
add_executable(mout main.cpp)
target_link_libraries(mout gflags glog)

目录如下

• 编译

• 运行

---

Example CMakeLists.txt of super-project which contains gflags source tree

https://www.nowcoder.com/discuss/652985?channel=-1&source_id=discuss_terminal_discuss_sim_nctrack&ncTraceId=cbbaed3185b94ea98d63e92d614e0334.1640.16214572630889822

• 目录结构

作者：fibonaccii
链接：https://www.nowcoder.com/discuss/652985?channel=-1&source_id=discuss_terminal_discuss_sim_nctrack&ncTraceId=cbbaed3185b94ea98d63e92d614e0334.1640.16214572630889822
来源：牛客网

$ tree -L 2
.
└── demo
    ├── CMakeLists.txt
    ├── build            # 目前是空的，用于后面编译输出
    ├── gflags           # 上面clone下来的代码
    └── main.cc          # 目前是空的

• CmakeLists.txt文件内容

cmake_minimum_required(VERSION 2.8.12)
project(gflags_demo)

add_subdirectory(gflags)                   # 添加子目录

add_executable(main main.cc)               # 生成目标文件 main
target_link_libraries(main gflags::gflags) # 链接到 gflags库

• main.cc内容

作者：fibonaccii
链接：https://www.nowcoder.com/discuss/652985?channel=-1&source_id=discuss_terminal_discuss_sim_nctrack&ncTraceId=cbbaed3185b94ea98d63e92d614e0334.1640.16214572630889822
来源：牛客网

#include 
#include 
 
DEFINE_bool(big_menu, true, "Include 'advance' option in the menu listing");
DEFINE_string(languages, "english, french, chinese", "comma-separated list of languages to offer in the 'lang' menu");
DEFINE_uint32(age, 10, "age");

int main(int argc, char** argv) {
    std::cout<

• 运行结果

作者：fibonaccii
链接：https://www.nowcoder.com/discuss/652985?channel=-1&source_id=discuss_terminal_discuss_sim_nctrack&ncTraceId=cbbaed3185b94ea98d63e92d614e0334.1640.16214572630889822
来源：牛客网

$  cd build && cmake .. && make     # 进入 demo/build 目录，再编译
$./main
big_menu: true
languages: english, french, chinese
age: 10

• 通过命令行设置参数

$  make
$ ./main -age 100 -languages "123456"
big_menu: true
languages: 123456
age: 100

对于命令行输入格式，gflags提供了四种格式，以age变量为例：

• ./main -age 100
• ./main -ag=100
• ./main --age 100
• ./main --age=100

使用--helpshort选项，就会显示这些变量的相关信息：

$ ./main --helpshort
main: Warning: SetUsageMessage() never called

Flags from /Users/self_study/Cpp/OpenSource/demo/main.cc:
  -age (age) type: uint32 default: 10
  -big_menu (Include 'advance' option in the menu listing) type: bool
    default: true
  -languages (comma-separated list of languages to offer in the 'lang' menu)
    type: string default: "english, french, chinese"

如果某个项目中使用了 gflags 定义了很多全局变量，分布在不同的文件中，你可以使用--helpfull选项来查看这些变量：

作者：fibonaccii
链接：https://www.nowcoder.com/discuss/652985?channel=-1&source_id=discuss_terminal_discuss_sim_nctrack&ncTraceId=cbbaed3185b94ea98d63e92d614e0334.1640.16214572630889822
来源：牛客网

% ./main --helpfull
main: Warning: SetUsageMessage() never called
 
  Flags from /Users/self_study/Cpp/OpenSource/demo/gflags/src/gflags.cc:
    -flagfile (load flags from file) type: string default: ""
    -fromenv (set flags from the environment [use 'export FLAGS_flag1=value'])
      type: string default: ""
    -tryfromenv (set flags from the environment if present) type: string
      default: ""
    -undefok (comma-separated list of flag names that it is okay to specify on
      the command line even if the program does not define a flag with that
      name.  IMPORTANT: flags in this list that have arguments MUST use the
      flag=value format) type: string default: ""
 
  Flags from /Users/self_study/Cpp/OpenSource/demo/gflags/src/gflags_completions.cc:
    -tab_completion_columns (Number of columns to use in output for tab
      completion) type: int32 default: 80
    -tab_completion_word (If non-empty, HandleCommandLineCompletions() will
      hijack the process and attempt to do bash-style command line flag
      completion on this value.) type: string default: ""
 
  Flags from /Users/self_study/Cpp/OpenSource/demo/gflags/src/gflags_reporting.cc:
    -help (show help on all flags [tip: all flags can have two dashes])
      type: bool default: false
    -helpfull (show help on all flags -- same as -help) type: bool
      default: false currently: true
    -helpmatch (show help on modules whose name contains the specified substr)
      type: string default: ""
    -helpon (show help on the modules named by this flag value) type: string
      default: ""
    -helppackage (show help on all modules in the main package) type: bool
      default: false
    -helpshort (show help on only the main module for this program) type: bool
      default: false
    -helpxml (produce an xml version of help) type: bool default: false
    -version (show version and build info and exit) type: bool default: false
 
 
 
  Flags from /Users/self_study/Cpp/OpenSource/demo/main.cc:
    -age (age) type: uint32 default: 10
    -big_menu (Include 'advance' option in the menu listing) type: bool
      default: true
    -languages (comma-separated list of languages to offer in the 'lang' menu)
      type: string default: "english, french, chinese"