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用Google的gflags优雅的解析命令行参数(一)

2017-05-29 16:54 405 查看

写了这么多年的Linux下C/C++代码，一直使用getopt_long来解析命令行参数，同时定义一个全局的struct来保存各个命令行参数的值。虽然用得比较“繁琐”，但也安于现状。最近突然发现了Google早在多年前就开源了一个解析命令行参数的“神器”gflags。赶紧来爽一把。

安装

1、去官网下载一个最新的版本(gflags-2.1.1.tar.gz)。

https://github.com/schuhschuh/gflags/archive/v2.1.1.tar.gz
2、现在流行cmake的构建方式，gflags的最新版本也改为使用cmake了。还好我最近也刚刚学习了cmake，算是跟上了潮流。有兴趣的话，可以看
《让cmake显示gcc/g++的编译信息》

[amcool@leoox soft]$ tar xzvf gflags-2.1.1.tar.gz
[amcool@leoox soft]$ cd gflags-2.1.1
[amcool@leoox gflags-2.1.1]$ mkdir build
[amcool@leoox gflags-2.1.1]$ cd build/
[amcool@leoox build]$ cmake .. -DCMAKE_INSTALL_PREFIX=/home/amcool/local/gflags-2.1.1
[amcool@leoox build]$ make
[amcool@leoox build]$ make install

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[amcool@leooxsoft]$tar
xzvf gflags-2.1.1.tar.gz

[amcool@leooxsoft]$cd
gflags-2.1.1
[amcool@l
4000
eooxgflags-2.1.1]$mkdir
build

[amcool@leooxgflags-2.1.1]$cd
build/
[amcool@leooxbuild]$cmake
..-DCMAKE_INSTALL_PREFIX=/home/amcool/local/gflags-2.1.1

[amcool@leooxbuild]$make
[amcool@leooxbuild]$make
install

就是这么简单，安装成功了。值得注意的是，我这里新建了一个build文件夹，即采用“外部构建”的方式。这样编译过程中产生的中间文件（比如.o文件）就都放在build里，不会“污染”gflags源码，做到干干净净。

爽一把

1、既然安装好了，那赶紧来写个简单的代码来爽一把。话不多说，代码才是王道！

// demo.cpp
#include <iostream>
#include <gflags/gflags.h>

using namespace std;

DEFINE_string(confPath, "../conf/setup.ini", "program configure file.");
DEFINE_int32(port, 9090, "program listen port");
DEFINE_bool(daemon, true, "run daemon mode");

int main(int argc, char** argv)
{
gflags::ParseCommandLineFlags(&argc, &argv, true);

cout << "confPath = " << FLAGS_confPath << endl;
cout << "port = " << FLAGS_port << endl;

if (FLAGS_daemon) {
cout << "run background ..." << endl;
}
else {
cout << "run foreground ..." << endl;
}

cout << "good luck and good bye!" << endl;

gflags::ShutDownCommandLineFlags();
return 0;
}

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// demo.cpp

#include <iostream>
#include <gflags/gflags.h>

usingnamespace
std;

DEFINE_string(confPath,"../conf/setup.ini","program
configure file.");

DEFINE_int32(port,9090,"program
listen port");
DEFINE_bool(daemon,true,"run
daemon mode");

intmain(intargc,char**argv)

{
  gflags::ParseCommandLineFlags(&argc,&argv,true);

  cout<<
"confPath = "<<
FLAGS_confPath<<
endl;

  cout<<
"port = "<<
FLAGS_port<<
endl;

  if(FLAGS_daemon){
    cout<<
"run background ..."<<
endl;

  }
  else{

    cout<<
"run foreground ..."<<
endl;
  }

  cout<<
"good luck and good bye!"<<
endl;

  gflags::ShutDownCommandLineFlags();

  return0;
}

2、很明显，接下来就是要编译了。这里直接用g++写一行命令就可以编译了。但是既然学了cmake，那就“大材小用”一次吧。

project(demo)
cmake_minimum_required(VERSION 2.8)
set(CMAKE_VERBOSE_MAKEFILE on)

include_directories("/home/amcool/local/gflags-2.1.1/include")
link_directories("/home/amcool/local/gflags-2.1.1/lib")

add_executable(demo demo.cpp)
target_link_libraries(demo gflags pthread)

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project(demo)

cmake_minimum_required(VERSION2.8)
set(CMAKE_VERBOSE_MAKEFILEon)

include_directories("/home/amcool/local/gflags-2.1.1/include")

link_directories("/home/amcool/local/gflags-2.1.1/lib")

add_executable(demodemo.cpp)
target_link_libraries(demogflags
pthread)

3、那当然就是编译了

[amcool@leoox demo]$ ls
CMakeLists.txt demo.cpp
[amcool@leoox demo]$ mkdir build
[amcool@leoox demo]$ cd build
[amcool@leoox build]$ cmake ..
[amcool@leoox build]$ ls
CMakeCache.txt CMakeFiles cmake_install.cmake Makefile
[amcool@leoox build]$ make
[amcool@leoox build]$ ls
CMakeCache.txt CMakeFiles cmake_install.cmake demo Makefile
[amcool@leoox build]$

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[amcool@leooxdemo]$ls

CMakeLists.txt  demo.cpp
[amcool@leooxdemo]$mkdir
build

[amcool@leooxdemo]$cd
build
[amcool@leooxbuild]$cmake
..

[amcool@leooxbuild]$ls
CMakeCache.txt  CMakeFiles  cmake_install.cmake  Makefile

[amcool@leooxbuild]$make
[amcool@leooxbuild]$ls

CMakeCache.txt  CMakeFiles  cmake_install.cmake  demo  Makefile
[amcool@leooxbuild]$

设定命令行参数

1、直接运行，得到的就是我们设定的默认参数。（聪明的你，结合代码一看，就知道参数的默认值是什么了）

[amcool@leoox build]$ ./demo
confPath = ../conf/setup.ini
port = 9090
run background ...
good luck and good bye!

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[amcool@leooxbuild]$./demo

confPath =../conf/setup.ini
port=
9090

run background...
goodluck
andgood
bye!

2、设定参数值

i）可以用 –参数名=参数值或者-参数名=参数值的方式来设定参数值。

ii）对于bool类型的参数，除了上述方式外，还可以用 –参数名的方式设定为true（即不带值），使用–no参数名的方式设定为false。为了统一，我建议都使用上面的第 i）种方法来设定参数。

[amcool@leoox build]$ ./demo --port=8888 --confPath=./setup.ini --daemon=true
confPath = ./setup.ini
port = 8888
run background ...
good luck and good bye!
[amcool@leoox build]$ ./demo -port=8888 -confPath=./setup.ini -daemon=false
confPath = ./setup.ini
port = 8888
run foreground ...
good luck and good bye!
[amcool@leoox build]$ ./demo -port=8888 -confPath=./setup.ini -daemon
confPath = ./setup.ini
port = 8888
run background ...
good luck and good bye!
[amcool@leoox build]$ ./demo -port=8888 -confPath=./setup.ini -nodaemon
confPath = ./setup.ini
port = 8888
run foreground ...
good luck and good bye!
[amcool@leoox build]$

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[amcool@leooxbuild]$./demo--port=8888--confPath=./setup.ini--daemon=true

confPath =./setup.ini
port=
8888

run background...
goodluck
andgood
bye!

[amcool@leooxbuild]$./demo-port=8888-confPath=./setup.ini-daemon=false
confPath=
./setup.ini

port =8888
runforeground
...

good luck andgood
bye!
[amcool@leooxbuild]$./demo-port=8888-confPath=./setup.ini-daemon

confPath =./setup.ini
port=
8888

run background...
goodluck
andgood
bye!

[amcool@leooxbuild]$./demo-port=8888-confPath=./setup.ini-nodaemon
confPath=
./setup.ini

port =8888
runforeground
...

good luck andgood
bye!
[amcool@leooxbuild]$

3、从文件读入“命令行”参数

如果我们的程序比较牛逼，配置项非常多，也就是说命令行参数很多，那你每次启动都要一个一个的输入，那岂不是很麻烦？gflags已经帮我们解决了，用
–flagfile=命令行文件的方式就可以了。你接着往下看，就明白了。param.cmd就是上面说的命令行文件。

[amcool@leoox build]$ vi param.cmd
--port=8888
--confPath=./setup.ini
--daemon=true
[amcool@leoox build]$ ./demo --flagfile=param.cmd
confPath = ./setup.ini
port = 8888
run background ...
good luck and good bye!
[amcool@leoox build]$

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[amcool@leooxbuild]$vi
param.cmd

--port=8888
--confPath=./setup.ini

--daemon=true
[amcool@leooxbuild]$./demo--flagfile=param.cmd

confPath =./setup.ini
port=
8888

run background...
goodluck
andgood
bye!

[amcool@leooxbuild]$

怎么样，这样就不怕参数配置错误了吧。保存到文件，每次启动，就很轻松了。

4、从环境变量读入参数值

gflags另外还给我们提供了 –fromenv 和 –tryfromenv 参数，通过这两个参数，我们的程序可以从环境变量中获取到具体的值。两者有什么不一样呢。你看到他们的区别仅仅是有无“try”，聪明的你一定猜到了。

–fromenv 从环境变量读取参数值 –fromenv=port,confPath 表明要从环境变量读取port,confPath两个参数的值。但是当无法从环境变量中获取到的时候，会报错，同时程序退出。【注意：gflags的变量名是 FLAGS_我们定义的参数名，开篇的代码里，估计细心的你已经发现了】
–tryfromenv 与–fromenv类似，当参数的没有在环境变量定义时，不退出。
也来一个例子，一看便明了。

[amcool@leoox build]$ ./demo --fromenv=port,confPath
ERROR: FLAGS_confPath not found in environment
ERROR: FLAGS_port not found in environment
[amcool@leoox build]$ ./demo --tryfromenv=port,confPath
confPath = ../conf/setup.ini
port = 9090
run background ...
good luck and good bye!
[amcool@leoox build]$ export FLAGS_confPath=./loveyou.ini
[amcool@leoox build]$ export FLAGS_port=36888
[amcool@leoox build]$ env | grep FLAGS
FLAGS_port=36888
FLAGS_confPath=./loveyou.ini
[amcool@leoox build]$
[amcool@leoox build]$ ./demo --fromenv=port,confPath
confPath = ./loveyou.ini
port = 36888
run background ...
good luck and good bye!
[amcool@leoox build]$

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[amcool@leooxbuild]$./demo--fromenv=port,confPath

ERROR:FLAGS_confPath
notfound
inenvironment
ERROR:FLAGS_port
notfound
inenvironment

[amcool@leooxbuild]$./demo--tryfromenv=port,confPath
confPath=
../conf/setup.ini

port =9090
runbackground
...

good luck andgood
bye!
[amcool@leooxbuild]$export
FLAGS_confPath=./loveyou.ini

[amcool@leooxbuild]$export
FLAGS_port=36888
[amcool@leooxbuild]$env
|grep
FLAGS

FLAGS_port=36888
FLAGS_confPath=./loveyou.ini

[amcool@leooxbuild]$
[amcool@leooxbuild]$./demo--fromenv=port,confPath

confPath =./loveyou.ini
port=
36888

run background...
goodluck
andgood
bye!

[amcool@leooxbuild]$

版本号和帮助信息

我们一般使用程序的时候，都离不开两个参数 –version 和 –help。来看看上面实现的demo能否支持呢？

[amcool@leoox build]$ ./demo --version
demo
[amcool@leoox build]$ ./demo --help
demo: Warning: SetUsageMessage() never called

Flags from /home/thrift/program/gflags/demo/demo.cpp:
-confPath (program configure file.) type: string
default: "../conf/setup.ini"
-daemon (run daemon mode) type: bool default: true
-port (program listen port) type: int32 default: 9090

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[amcool@leooxbuild]$./demo--version

demo
[amcool@leooxbuild]$./demo--help

demo:Warning:SetUsageMessage()never
called

Flags from/home/thrift/program/gflags/demo/demo.cpp:
-confPath(program
configurefile.)type:string

default:"../conf/setup.ini"
-daemon(run
daemonmode)type:bool
default:true

-port(program
listenport)type:int32
default:9090

哈，help支持了，但是version没支持，而且help信息里面还有waring。没关系，我们可以用 SetVersionString() 和 SetUsageMessage() 方法来满足需求。修改后的代码如下：

【注意：SetVersionString() 和 SetUsageMessage() 一定要在 ParseCommandLineFlags() 之前设定。】

#include <iostream>
#include <gflags/gflags.h>

using namespace std;

DEFINE_string(confPath, "../conf/setup.ini", "program configure file.");
DEFINE_int32(port, 9090, "program listen port");
DEFINE_bool(daemon, true, "run daemon mode");

int main(int argc, char** argv)
{
gflags::SetVersionString("1.0.0.0");
gflags::SetUsageMessage("Usage : ./demo ");
gflags::ParseCommandLineFlags(&argc, &argv, true);

cout << "confPath = " << FLAGS_confPath << endl;
cout << "port = " << FLAGS_port << endl;

if (FLAGS_daemon) {
cout << "run background ..." << endl;
}
else {
cout << "run foreground ..." << endl;
}

cout << "good luck and good bye!" << endl;

gflags::ShutDownCommandLineFlags();
return 0;
}

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#include <iostream>

#include <gflags/gflags.h>

using namespacestd;

DEFINE_string(confPath,"../conf/setup.ini","program
configure file.");
DEFINE_int32(port,9090,"program
listen port");

DEFINE_bool(daemon,true,"run
daemon mode");

int main(intargc,char**argv)
{

  gflags::SetVersionString("1.0.0.0");
  gflags::SetUsageMessage("Usage
: ./demo ");

  gflags::ParseCommandLineFlags(&argc,&argv,true);

  cout<<
"confPath = "<<
FLAGS_confPath<<
endl;
  cout<<
"port = "<<
FLAGS_port<<
endl;

  if(FLAGS_daemon){

    cout<<
"run background ..."<<
endl;
  }

  else{
    cout<<
"run foreground ..."<<
endl;

  }

  cout<<
"good luck and good bye!"<<
endl;

  gflags::ShutDownCommandLineFlags();
  return0;

}

可以来炫一把了：

[amcool@leoox build]$ ./demo --version
demo version 1.0.0.0
[amcool@leoox build]$ ./demo --help
demo: Usage : ./demo

Flags from /home/amcool/program/gflags/demo/demo.cpp:
-confPath (program configure file.) type: string
default: "../conf/setup.ini"
-daemon (run daemon mode) type: bool default: true
-port (program listen port) type: int32 default: 9090

Flags from /home/amcool/soft/gflags-2.1.1/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 /home/amcool/soft/gflags-2.1.1/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 /home/amcool/soft/gflags-2.1.1/src/gflags_reporting.cc:
-help (show help on all flags [tip: all flags can have two dashes])
type: bool default: false currently: true
-helpfull (show help on all flags -- same as -help) type: bool
default: false
-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
[amcool@leoox build]$

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[amcool@leooxbuild]$./demo--version

demo version1.0.0.0
[amcool@leooxbuild]$./demo--help

demo:Usage
:./demo

  Flags from/home/amcool/program/gflags/demo/demo.cpp:
    -confPath(program
configurefile.)type:string

      default:"../conf/setup.ini"
    -daemon(run
daemonmode)type:bool
default:true

    -port(program
listenport)type:int32
default:9090

  Flags from/home/amcool/soft/gflags-2.1.1/src/gflags.cc:
    -flagfile(load
flagsfrom file)type:string
default:""

    -fromenv(set
flagsfrom the
environment[use'export FLAGS_flag1=value'])
      type:string
default:""

    -tryfromenv(set
flagsfrom the
environmentif
present)type:string
      default:""

    -undefok(comma-separatedlist
of flagnames
that itis
okayto
specifyon
      thecommand
line evenif
theprogram does
notdefine
aflag
with that

      name.  IMPORTANT:flags
inthis
listthat have
argumentsMUST
usethe
      flag=valueformat)type:string
default:""

  Flagsfrom
/home/amcool/soft/gflags-2.1.1/src/gflags_completions.cc:

    -tab_completion_columns(Number
ofcolumns touse
inoutput
fortab
      completion)type:int32
default:80

    -tab_completion_word(Ifnon-empty,HandleCommandLineCompletions()will
      hijackthe
process andattempt
todo
bash-stylecommand
line flag

      completion onthis
value.)type:string
default:""

  Flags from/home/amcool/soft/gflags-2.1.1/src/gflags_reporting.cc:
    -help(show
helpon all
flags[tip:all
flags canhave
two dashes])

      type:bool
default:false
currently:true
    -helpfull(show
helpon all
flags--
sameas
-help)type:bool

      default:false
    -helpmatch(show
helpon modules
whosename contains
the specified
substr)

      type:string
default:""
    -helpon(show
helpon the
modulesnamed by
thisflag
value)type:string

      default:""
    -helppackage(show
helpon all
modulesin
themain package)type:bool

      default:false
    -helpshort(show
helpon only
themain module
forthis
program)type:bool

      default:false
    -helpxml(produce
anxml version
ofhelp)type:bool
default:false

    -version(show
versionand
buildinfo andexit)type:bool
default:false
[amcool@leooxbuild]$

简单讲解如何使用gflags进行编码

有了上面的演示和代码展示，想必大家对gflags有了比较直观的认识。做了这么久的前戏，接下来，终于可以深入了解啦。请看下文《用Google的gflags轻松的编码解析命令行参数》。

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