区块链研习社比特币源码研读班
今天研读第五步，参数解析

一总体结构图

image.png

二今天阅读的代码段

   //《1 解析main函数的命令行参数，放入gArgs变量中
    gArgs.ParseParameters(argc, argv);

    if (gArgs.IsArgSet("-?") || gArgs.IsArgSet("-h") ||  gArgs.IsArgSet("-help") || gArgs.IsArgSet("-version"))
    {
        //《2 打印信息增加包名，版本信息
        std::string strUsage = strprintf(_("%s Daemon"), _(PACKAGE_NAME)) + " " + _("version") + " " + FormatFullVersion() + "\n";

        
        if (gArgs.IsArgSet("-version"))
        {
            //《3 打印信息增加当前证书信息
            strUsage += FormatParagraph(LicenseInfo());
        }
        else
        {
           //《4 增加命令行参数使用帮助信息
            strUsage += "\n" + _("Usage:") + "\n" +
                  "  bitcoind [options]                     " + strprintf(_("Start %s Daemon"), _(PACKAGE_NAME)) + "\n";

            strUsage += "\n" + HelpMessage(HMM_BITCOIND);
        }

        fprintf(stdout, "%s", strUsage.c_str());
        return true;
    }

    try
    {
        //《5 检查区块数据保存目录是否存在
        if (!fs::is_directory(GetDataDir(false)))
        {
            fprintf(stderr, "Error: Specified data directory \"%s\" does not exist.\n", gArgs.GetArg("-datadir", "").c_str());
            return false;
        }
         //《6 读取配置文件
        try
        {
            gArgs.ReadConfigFile(gArgs.GetArg("-conf", BITCOIN_CONF_FILENAME));
        } catch (const std::exception& e) {
            fprintf(stderr,"Error reading configuration file: %s\n", e.what());
            return false;
        }

        //《7  检查测试参数有效
        try {
            SelectParams(ChainNameFromCommandLine());
        } catch (const std::exception& e) {
            fprintf(stderr, "Error: %s\n", e.what());
            return false;
        }

        // 《8  检查命令行的引导参数有异常，必须带- 或 /
        for (int i = 1; i < argc; i++) {
            if (!IsSwitchChar(argv[i][0])) {
                fprintf(stderr, "Error: Command line contains unexpected token '%s', see bitcoind -h for a list of options.\n", argv[i]);
                exit(EXIT_FAILURE);
            }
        }

三 分析
《1 解析main函数的命令行参数，放入gArgs变量中

    gArgs.ParseParameters(argc, argv);

    gArgs.ParseParameters(argc, argv);  
（1）argc为main函数传入的参数个数
（2）argv为main函数传入的参数字符串的二维指针

此函数定义在util.cpp中
void ArgsManager::ParseParameters(int argc, const char* const argv[])

 函数意图是处理形如 -externalip=<ip> 这类格式的参数，写入全局参数map中mapArgs中，后面使用

《2 打印信息增加包名，版本信息

        std::string strUsage = strprintf(_("%s Daemon"), _(PACKAGE_NAME)) + " " + _("version") + " " + FormatFullVersion() + "\n";

其中 
（1）PACKAGE_NAME是一个宏定义， 在xxx中。内容为"Bitcoin Core"
（2）FormatFullVersion()返回当前版本，见cientversion.cpp中
std::string FormatFullVersion()
{
    return CLIENT_BUILD;
}

const std::string CLIENT_BUILD(BUILD_DESC CLIENT_VERSION_SUFFIX);   //此处用两个宏构造版本号CLIENT_BUILD


（1）BUILD_DESC  =》 
#ifndef BUILD_DESC
#ifdef BUILD_SUFFIX
#define BUILD_DESC BUILD_DESC_WITH_SUFFIX(CLIENT_VERSION_MAJOR, CLIENT_VERSION_MINOR, CLIENT_VERSION_REVISION, CLIENT_VERSION_BUILD, BUILD_SUFFIX)
#elif defined(GIT_COMMIT_ID)
#define BUILD_DESC BUILD_DESC_FROM_COMMIT(CLIENT_VERSION_MAJOR, CLIENT_VERSION_MINOR, CLIENT_VERSION_REVISION, CLIENT_VERSION_BUILD, GIT_COMMIT_ID)
#else
#define BUILD_DESC BUILD_DESC_FROM_UNKNOWN(CLIENT_VERSION_MAJOR, CLIENT_VERSION_MINOR, CLIENT_VERSION_REVISION, CLIENT_VERSION_BUILD)
#endif
#endif

//这四个宏,见bitcoin-config.h

/* Version Build */
#define CLIENT_VERSION_BUILD 0

/* Major version */
#define CLIENT_VERSION_MAJOR 0

/* Minor version */
#define CLIENT_VERSION_MINOR 15

/* Build revision */
#define CLIENT_VERSION_REVISION 0

注意：bitcoin-config.h该文件在我们下载的源码中一开始是不存在的，需经过对源码进行./configure命令后才能生成。源码的./configure过程可参见菜菜子的[《聊聊比特币(Bitcoin)客户端源码编译那些事》](http://www.jianshu.com/p/8b4ebd0e4b3d)一文。

（2）CLIENT_VERSION_SUFFIX=》
#define CLIENT_VERSION_SUFFIX ""

《3 打印信息增加搬迁证书信息信息

            strUsage += FormatParagraph(LicenseInfo());

（1）
FormatParagraph函数声明在bitcoin/src/utilstrencodings.h中
/**
 * Format a paragraph of text to a fixed width, adding spaces for
 * indentation to any added line.
 */将文本段落格式设置为固定宽度, 将缩进的空格添加到任何添加的行中
std::string FormatParagraph(const std::string& in, size_t width = 79, size_t indent = 0);

（2）LicenseInfo函数在init.h中，主要返回版权信息（MIT协议等等）
/** Returns licensing information (for -version) */
std::string LicenseInfo();

std::string LicenseInfo()
{
    const std::string URL_SOURCE_CODE = "<https://github.com/bitcoin/bitcoin>";
    const std::string URL_WEBSITE = "<https://bitcoincore.org>";

    return CopyrightHolders(strprintf(_("Copyright (C) %i-%i"), 2009, COPYRIGHT_YEAR) + " ") + "\n" +
           "\n" +
           strprintf(_("Please contribute if you find %s useful. "
                       "Visit %s for further information about the software."),
               PACKAGE_NAME, URL_WEBSITE) +
           "\n" +
           strprintf(_("The source code is available from %s."),
               URL_SOURCE_CODE) +
           "\n" +
           "\n" +
           _("This is experimental software.") + "\n" +
           strprintf(_("Distributed under the MIT software license, see the accompanying file %s or %s"), "COPYING", "<https://opensource.org/licenses/MIT>") + "\n" +
           "\n" +
           strprintf(_("This product includes software developed by the OpenSSL Project for use in the OpenSSL Toolkit %s and cryptographic software written by Eric Young and UPnP software written by Thomas Bernard."), "<https://www.openssl.org>") +
           "\n";
}

《4 增加命令行参数使用帮助信息

            strUsage += "\n" + _("Usage:") + "\n" +
                  "  bitcoind [options]                     " + strprintf(_("Start %s Daemon"), _(PACKAGE_NAME)) + "\n";
strUsage += "\n" + HelpMessage(HMM_BITCOIND);

（1）PACKAGE_NAME为包名，见
PACKAGE_NAME的定义位于src/config/bitcoin-config.h中
#define PACKAGE_NAME "Bitcoin Core"

注意：bitcoin-config.h该文件在我们下载的源码中一开始是不存在的，需经过对源码进行./configure命令后才能生成。源码的./configure过程可参见菜菜子的[《聊聊比特币(Bitcoin)客户端源码编译那些事》](http://www.jianshu.com/p/8b4ebd0e4b3d)一文。


（2）HelpMessage，在init.cpp。根据消息模式不同，返回不同的帮助字符串
std::string HelpMessage(HelpMessageMode mode)

/** The help message mode determines what help message to show */
enum HelpMessageMode {
    HMM_BITCOIND,     //推理是命令行模式
    HMM_BITCOIN_QT //推理是qt界面模式
};