转载： http://www.leoox.com/?p=270
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。
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 1 2 3 4 5 6 7 [ 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 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。
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; } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 // 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 ; }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) 1 2 3 4 5 6 7 8 9 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 )
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]$ 1 2 3 4 5 6 7 8 9 10 11 [ 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 ] $
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! 1 2 3 4 5 [ amcool @ leoox build ] $ . / demo confPath = . . / conf / setup . ini port = 9090 run background . . . good luck and good 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]$ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 [ 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 ] $
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]$ 1 2 3 4 5 6 7 8 9 10 [ 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 ] $怎么样，这样就不怕参数配置错误了吧。保存到文件，每次启动，就很轻松了。
4、从环境变量读入参数值
gflags另外还给我们提供了 –fromenv 和 –tryfromenv 参数，通过这两个参数，我们的程序可以从环境变量中获取到具体的值。两者有什么不一样呢。你看到他们的区别仅仅是有无“try”，聪明的你一定猜到了。
–fromenv 从环境变量读取参数值 –fromenv=port,confPath 表明要从环境变量读取port,confPath两个参数的值。但是当无法从环境变量中获取到的时候，会报错，同时程序退出。【注意：gflags的变量名是 FLAGS_我们定义的参数名，开篇的代码里，估计细心的你已经发现了】–tryfromenv 与–fromenv类似，当参数的没有在环境变量定义时，不退出。也来一个例子，一看便明了。
[amcool@leoox build]$ ./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]$ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 [ 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 ] $
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 1 2 3 4 5 6 7 8 9 10 [ 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
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; } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 #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 ; }
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]$ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 [ 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 ] $
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》。
