Google gflags使用说明

一、gflags是什么

gflags是google的一个开源的处理命令行参数的库，使用c++开发，具备python接口。

 

二、下载安装

1.下载：https://gflags.github.io/gflags/

2.解压安装

tar zxvf gflags-2.0.tar.gz && cd gflags-2.0 && ./configure && make && make install

这时 gflags 库会默认安装在 /usr/local/lib/ 下，头文件放在 /usr/local/include/gflags/ 中。

 

三、gflags支持以下类型

将需要的命令行参数使用gflags的宏，DEFINE_xxxxx(变量名，默认值，help-string) 定义在文件当中。

• DEFINE_bool: boolean
• DEFINE_int32: 32-bit integer
• DEFINE_int64: 64-bit integer
• DEFINE_uint64: unsigned 64-bit integer
• DEFINE_double: double
• DEFINE_string: C++ string

 

四、若需要在其它文件中使用gflags的变量，可以使用宏定义声明下：DECLARE_xxx(变量名)，之后在代码中便可以使用FLAGS_XXX格式使用命令行的参数了。

 

五、定制自己的help和version信息

• version信息：使用google::SetVersionString(const std::string& usage)设定，使用google::VersionString访问
• help信息：使用google::SetUsageMessage(const std::string& usage)设定，使用google::ProgramUsage访问
• 注意：google::SetUsageMessage和google::SetVersionString必须在google::ParseCommandLineFlags之前执行

     一般在main函数的头几行编写这些信息。

 

六、特殊的flags

--flagfile：--flagfile=f 告诉commandlineflags从这个文件中读取出所有的命令行参数，f文件应该有特殊的格式要求，是一个参数的list，每行一个参数，格式如下：

--languages=english

（更详细的介绍请参考官网 https://gflags.github.io/gflags/）

 

七、简单使用

#include <iostream>
#include <gflags/gflags.h>
using namespace std;
using namespace google;

DEFINE_string(host, "127.0.0.1", "the server port"); 
DEFINE_int32(port, 9090, "program listen port");
DEFINE_bool(sign, true, "switch mode");

static std::string g_version;
static std::string g_help;

std::string& getVersion() {
    g_version = "0.1";
    return g_version;
}

std::string& getHelp() {
    g_help = "help info";
    return g_help;
}

int main(int argc, char** argv) {
    google::SetVersionString(getVersion());
    google::SetUsageMessage(getHelp());
    google::ParseCommandLineFlags(&argc, &argv, true);
    cout << "host = " << FLAGS_host << endl;
    cout << "port = " << FLAGS_port << endl;
    if (FLAGS_sign) {
      cout << "sign is true ..." << endl;
    }   
    else {
      cout << "sign is false ..." << endl;
    }   
    google::ShutDownCommandLineFlags();
    return 0;
}

编译，使用makefile

GFLAGS_DIR = /usr/local/include/gflags/
LIB_DIR = /usr/local/lib/
a.out: simple_flags.cpp
        g++ -I${GFLAGS_DIR} -L${LIB_DIR} simple_flags.cpp -lgflags
clean:
        $(RM) -r a.out

执行，不给参数：

./a.out

host = 127.0.0.1
port = 9090
sign is true ...

给参数：

./a.out -host 172.168.16.8 -port 2356

host = 172.168.16.8
port = 2356
sign is true ...

使用文件file,文件内容如下：

--host=172.16.12.10
--port=8955
--sign=false

 执行：

./a.out --flagfile=flag

host = 172.16.12.10
port = 8955
sign is false ...

查看version和help信息：

./a.out -version

a.out version 0.1

./a.out -help

a.out: help info

  Flags from simple_flags.cpp:
    -host (the server port) type: string default: "127.0.0.1"
    -port (program listen port) type: int32 default: 9090
    -sign (switch mode) type: bool default: true

  Flags from 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 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 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

 

八、多文件引用（DECLARE_XXX使用）

gflagdef.h文件

#ifndef _GFLAG_DEF_H_
#define _GFLAG_DEF_H_
#include <gflags/gflags.h>

DECLARE_int32(port);
DECLARE_string(host);
DECLARE_bool(sign);

#endif

 

gflagdef.cpp文件

#include <gflags/gflags.h>
DEFINE_int32(port, 9001, "The server port");
DEFINE_string(host, "127.0.0.1", "listen port");
DEFINE_bool(sign, true, "switch mode");

 

main.cpp文件

#include <iostream>
#include "gflagdef.h"
using namespace std;
int main(int argc, char** argv) {
    google::ParseCommandLineFlags(&argc, &argv, true);
    cout << "host = " << FLAGS_host << endl;
    cout << "port = " << FLAGS_port << endl;
    if (FLAGS_sign) {
        cout << "sign is true ..." << endl;
    }   
    else {
        cout << "sign is false ..." << endl;
    }   
    google::ShutDownCommandLineFlags();
    return 0;
}

 

makefile文件

GFLAGS_DIR = /usr/local/include/gflags/
LIB_DIR = /usr/local/lib/
main: main.o flag.o
        g++ main.o flag.o -o main -lgflags
main.o: main.cpp
        g++ -c -I${GFLAGS_DIR} -L${LIB_DIR} main.cpp -lgflags -o main.o
flag.o: gflagdef.cpp
        g++ -c -I${GFLAGS_DIR} -L${LIB_DIR} gflagdef.cpp -lgflags -o flag.o
clean:
        $(RM) -r main *.o

 

编译&&执行：make&&./main

host = 127.0.0.1
port = 9001
sign is true ...