转载： http://www.leoox.com/?p=275

有了上文《用Google的gflags优雅的解析命令行参数》到位的前戏，已经知道gflags是何方“尤物”了。接下来就该深入一下了。

 

   支持的参数类型

gflags支持的类型有bool，int32，int64，uint64，double和string。可以说这些基本类型大体上满足了我们的需求。

DEFINE_bool: booleanDEFINE_int32: 32-bit integerDEFINE_int64: 64-bit integerDEFINE_uint64: unsigned 64-bit integerDEFINE_double: doubleDEFINE_string: C++ string

比如上文中，我就定义了confPath, port, daemon三个命令行参数，回顾一下：

DEFINE_string(confPath, "../conf/setup.ini", "program configure file."); DEFINE_int32(port, 9090, "program listen port"); DEFINE_bool(daemon, true, "run daemon mode"); 1 2 3 DEFINE_string ( confPath , "../conf/setup.ini" , "program configure file." ) ; DEFINE_int32 ( port , 9090 , "program listen port" ) ; DEFINE_bool ( daemon , true , "run daemon mode" ) ;

稍微讲解一下：

第一个字段 confPath就是命令行里要输入的参数名，比如 –confPath=./love.ini第二个字段”../conf/setup.ini”，就是如果命令行里没指定这个参数，那默认值就是 ../conf/setup.ini第三个字段”program configure file.”，就是这个参数的帮助说明信息，当用户输入 –hlep 的时候，会显示出来。

 

   代码中使用这个变量

以前我们使用getopt_long函数来自己解析命令行参数的时候，都得内部定义一个变量来保存从命令行得到的值。后续就可以使用这个变量来完成相应的代码逻辑。那其实，DEFINE_string等“指令”就相当于定义了变量，只不过变量名多了个前缀 “FLAGS_“。即，我们可以在代码里面直接操作FLAGS_confPath，FLAGS_port，FLAGS_port，FLAGS_daemon这三个变量。

 

    解析命令行参数

gflags是使用ParseCommandLineFlags这个方法来完成命令行参数的解析的。具体如下：

gflags::ParseCommandLineFlags(&argc, &argv, true); 1 gflags :: ParseCommandLineFlags ( &argc , &argv , true ) ;

一目了然，唯一值得注意的就是第三个参数了。如果设置为true，gflags就会移除解析过的参数。即argc, argv就会变了。否则gflags还会保持这些参数继续留在argc，argv中。但是参数的顺序有可能会发生变化。

如果不好理解的话，没关系，来一段代码就明白什么意思了。

#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) { for (int i = 0; i < argc; i++) { printf("argv[%d] = %s\n", i, argv[i]); } printf("---------------here--------------\n"); gflags::SetVersionString("1.0.0.0"); gflags::SetUsageMessage("Usage : ./demo "); gflags::ParseCommandLineFlags(&argc, &argv, true); for (int i = 0; i < argc; i++) { printf("argv[%d] = %s\n", i, argv[i]); } printf("---------------there--------------\n"); 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 31 32 33 34 35 36 37 38 39 40 #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 ) {    for ( int i = 0 ; i < argc ; i ++ ) {      printf ( "argv[%d] = %s\n" , i , argv [ i ] ) ;    }    printf ( "---------------here--------------\n" ) ;      gflags :: SetVersionString ( "1.0.0.0" ) ;    gflags :: SetUsageMessage ( "Usage : ./demo " ) ;    gflags :: ParseCommandLineFlags ( &argc , &argv , true ) ;    for ( int i = 0 ; i < argc ; i ++ ) {      printf ( "argv[%d] = %s\n" , i , argv [ i ] ) ;    }    printf ( "---------------there--------------\n" ) ;      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 ; }

 

运行后，看一下true的情况：

[amcool@leoox build]$ ./demo --port=8888 --confPath=./happy.ini --daemon argv[0] = ./demo argv[1] = --port=8888 argv[2] = --confPath=./happy.ini argv[3] = --daemon ---------------here-------------- argv[0] = ./demo ---------------there-------------- confPath = ./happy.ini port = 8888 run background ... good luck and good bye! 1 2 3 4 5 6 7 8 9 10 11 12 [ amcool @ leoox build ] $ . / demo -- port = 8888 -- confPath = . / happy . ini -- daemon argv [ 0 ] = . / demo argv [ 1 ] = -- port = 8888 argv [ 2 ] = -- confPath = . / happy . ini argv [ 3 ] = -- daemon -- -- -- -- -- -- -- - here -- -- -- -- -- -- -- argv [ 0 ] = . / demo -- -- -- -- -- -- -- - there -- -- -- -- -- -- -- confPath = . / happy . ini port = 8888 run background . . . good luck and good bye !

 

修改为false，在运行一下的情况：

 

[amcool@leoox build]$ ./demo --port=8888 --confPath=./happy.ini --daemon argv[0] = ./demo argv[1] = --port=8888 argv[2] = --confPath=./happy.ini argv[3] = --daemon ---------------here-------------- argv[0] = ./demo argv[1] = --port=8888 argv[2] = --confPath=./happy.ini argv[3] = --daemon ---------------there-------------- confPath = ./happy.ini port = 8888 run background ... good luck and good bye! 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 [ amcool @ leoox build ] $ . / demo -- port = 8888 -- confPath = . / happy . ini -- daemon   argv [ 0 ] = . / demo argv [ 1 ] = -- port = 8888 argv [ 2 ] = -- confPath = . / happy . ini argv [ 3 ] = -- daemon -- -- -- -- -- -- -- - here -- -- -- -- -- -- -- argv [ 0 ] = . / demo argv [ 1 ] = -- port = 8888 argv [ 2 ] = -- confPath = . / happy . ini argv [ 3 ] = -- daemon -- -- -- -- -- -- -- - there -- -- -- -- -- -- -- confPath = . / happy . ini port = 8888 run background . . . good luck and good bye !

 

    参数检查

按照以前的习惯，我们可以获取到所有参数的值后，再在代码里面进行判断这个参数是否是我们想要的。比如，我们需要端口是36800 到 36888之间的，那我们可以这样检查。

if (FLAGS_port < 36800 || FLAGS_port > 36888) { printf("port must [36800, 36888]\n"); return -1; } 1 2 3 4 if ( FLAGS_port < 36800 || FLAGS_port > 36888 ) {      printf ( "port must [36800, 36888]\n" ) ;      return - 1 ; }

 

当然gflags里面建议使用 RegisterFlagValidator 这个方法来做参数检查。参数不通过的时候，程序是启动失败的。

static bool ValidatePort(const char* flagname, gflags::int32 value) { if (value >= 36800 && value <= 36888) { printf("param(%s) = (%d) is valid!\n", flagname, value); return true; } printf("param(%s) = (%d) is invalid!\n", flagname, value); return false; } DEFINE_int32(port, 36810, "program listen port"); static const bool validPort = gflags::RegisterFlagValidator(&FLAGS_port, &ValidatePort); 1 2 3 4 5 6 7 8 9 10 11 static bool ValidatePort ( const char * flagname , gflags :: int32 value ) {    if ( value >= 36800 && value <= 36888 ) {      printf ( "param(%s) = (%d) is valid!\n" , flagname , value ) ;      return true ;    }      printf ( "param(%s) = (%d) is invalid!\n" , flagname , value ) ;    return false ; } DEFINE_int32 ( port , 36810 , "program listen port" ) ; static const bool validPort = gflags :: RegisterFlagValidator ( &FLAGS_port , &ValidatePort ) ;

 

运行一下，看看效果：

[amcool@leoox build]$ ./demo --port=36889 --confPath=./happy.ini --daemon param(port) = (36889) is invalid! param(port) = (36810) is valid! ERROR: failed validation of new value '36889' for flag 'port' 1 2 3 4 [ amcool @ leoox build ] $ . / demo -- port = 36889 -- confPath = . / happy . ini -- daemon param ( port ) = ( 36889 ) is invalid ! param ( port ) = ( 36810 ) is valid ! ERROR : failed validation of new value '36889' for flag 'port'

 

【疑问】：我们手动指定端口36889不合法，默认的36810合法。怎么让gflags当发现参数不合法的时候，使用合法的默认参数呢？！

 

    其他代码文件使用参数变量

正常来说，我们的代码不可能只有1个cpp，还会有很多模块。而每个模块可能会使用到不同的参数值。所以我们之前在demo.cpp定义的参数变量（比如FLAGS_port），在其他模块怎么引用和使用呢？so easy，与DEFINE相对应的有DECLARE。声明一下，就可以使用了。

DECLARE_bool: booleanDECLARE_int32: 32-bit integerDECLARE_int64: 64-bit integerDECLARE_uint64: unsigned 64-bit integerDECLARE_double: doubleDECLARE_string: C++ string

 

来一段简单的代码，就一目了然啦。

     示例代码目录结构

[amcool@leoox demo]$ tree . |-- CMakeLists.txt |-- build |-- demo.cpp |-- logic.cpp `-- logic.h 1 directory, 4 files [amcool@leoox demo]$ 1 2 3 4 5 6 7 8 9 10 [ amcool @ leoox demo ] $ tree . | -- CMakeLists . txt | -- build | -- demo . cpp | -- logic . cpp ` -- logic . h   1 directory , 4 files [ amcool @ leoox demo ] $

 

    logic.h

#ifndef _LEOOX_LOGIC_H_ #define _LEOOX_LOGIC_H_ #include <iostream> #include <gflags/gflags.h> using namespace std; DECLARE_string(confPath); DECLARE_int32(port); DECLARE_bool(daemon); int process(); #endif 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 #ifndef _LEOOX_LOGIC_H_ #define _LEOOX_LOGIC_H_   #include <iostream> #include <gflags/gflags.h> using namespace std ;   DECLARE_string ( confPath ) ; DECLARE_int32 ( port ) ; DECLARE_bool ( daemon ) ;   int process ( ) ;   #endif

 

     logic.cpp

#include "logic.h" int process() { printf("----------------- process start ---------------\n"); cout << "confPath = " << FLAGS_confPath << endl; cout << "port = " << FLAGS_port << endl; if (FLAGS_daemon) { cout << "run background ..." << endl; } else { cout << "run foreground ..." << endl; } printf("----------------- process end ---------------\n"); return 0; } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 #include "logic.h"   int process ( ) {    printf ( "----------------- process start ---------------\n" ) ;    cout << "confPath = " << FLAGS_confPath << endl ;    cout << "port = " << FLAGS_port << endl ;    if ( FLAGS_daemon ) {      cout << "run background ..." << endl ;    }    else {      cout << "run foreground ..." << endl ;    }    printf ( "----------------- process end ---------------\n" ) ;      return 0 ; }

 

   demo.cpp

#include "logic.h" DEFINE_string(confPath, "../conf/setup.ini", "program configure file."); DEFINE_bool(daemon, true, "run daemon mode"); static bool ValidatePort(const char* flagname, gflags::int32 value) { if (value >= 36800 && value <= 36888) { printf("param(%s) = (%d) is valid!\n", flagname, value); return true; } printf("param(%s) = (%d) is invalid!\n", flagname, value); return false; } DEFINE_int32(port, 36810, "program listen port"); static const bool validPort = gflags::RegisterFlagValidator(&FLAGS_port, &ValidatePort); int main(int argc, char** argv) { gflags::SetVersionString("1.0.0.0"); gflags::SetUsageMessage("Usage : ./demo "); gflags::ParseCommandLineFlags(&argc, &argv, false); process(); 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 31 #include "logic.h" DEFINE_string ( confPath , "../conf/setup.ini" , "program configure file." ) ;   DEFINE_bool ( daemon , true , "run daemon mode" ) ;   static bool ValidatePort ( const char * flagname , gflags :: int32 value ) {    if ( value >= 36800 && value <= 36888 ) {      printf ( "param(%s) = (%d) is valid!\n" , flagname , value ) ;      return true ;    }      printf ( "param(%s) = (%d) is invalid!\n" , flagname , value ) ;    return false ; } DEFINE_int32 ( port , 36810 , "program listen port" ) ; static const bool validPort = gflags :: RegisterFlagValidator ( &FLAGS_port , &ValidatePort ) ; int main ( int argc , char * * argv ) {    gflags :: SetVersionString ( "1.0.0.0" ) ;    gflags :: SetUsageMessage ( "Usage : ./demo " ) ;    gflags :: ParseCommandLineFlags ( &argc , &argv , false ) ;      process ( ) ;    cout << "good luck and good bye!" << endl ;    gflags :: ShutDownCommandLineFlags ( ) ;    return 0 ; }

 

    CMakeLists.txt

project(demo) cmake_minimum_required(VERSION 2.8) set(CMAKE_VERBOSE_MAKEFILE on) include_directories(".") include_directories("/home/leoox/local/gflags-2.1.1/include") link_directories("/home/leoox/local/gflags-2.1.1/lib") add_executable(demo demo.cpp logic.cpp) target_link_libraries(demo gflags pthread) 1 2 3 4 5 6 7 8 9 10 project ( demo ) cmake_minimum_required ( VERSION 2.8 ) set ( CMAKE_VERBOSE_MAKEFILE on )   include_directories ( "." ) include_directories ( "/home/leoox/local/gflags-2.1.1/include" ) link_directories ( "/home/leoox/local/gflags-2.1.1/lib" )   add_executable ( demo demo .cpp logic .cpp ) target_link_libraries ( demo gflags pthread )

 

    运行结果

[amcool@leoox build]$ ./demo --port=36850 --confPath=./love.ini param(port) = (36850) is valid! param(port) = (36850) is valid! ----------------- process start --------------- confPath = ./love.ini port = 36850 run background ... ----------------- process end --------------- good luck and good bye! [amcool@leoox build]$ 1 2 3 4 5 6 7 8 9 10 [ amcool @ leoox build ] $ . / demo -- port = 36850 -- confPath = . / love . ini param ( port ) = ( 36850 ) is valid ! param ( port ) = ( 36850 ) is valid ! -- -- -- -- -- -- -- -- - process start -- -- -- -- -- -- -- - confPath = . / love . ini port = 36850 run background . . . -- -- -- -- -- -- -- -- - process end -- -- -- -- -- -- -- - good luck and good bye ! [ amcool @ leoox build ] $

 

至此，Google的强大的开源组件之一的“gflags”，就算完成了深入浅出的学习了。自己以后可以把getopt_long深藏功与名了。哈哈。