五分钟快速入门

本教程使用XML。注意，这个库不是专门绑定到XML的，而是可以使用任何其他支持的格式(如INI或JSON)。之所以选择XML，是因为作者认为很多人都熟悉XML。

假设我们正在为某个应用程序编写一个日志系统，并且需要在程序启动时从文件中读取日志配置。带有日志配置的文件如下所示:

<debug>
    <filename>debug.log</filename>
    <modules>
        <module>Finance</module>
        <module>Admin</module>
        <module>HR</module>
    </modules>
    <level>2</level>
</debug>

它包含日志文件名、启用日志记录的模块列表和调试级别值。

我们需要包含的头文件：

#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/xml_parser.hpp>
#include <boost/foreach.hpp>
#include <string>
#include <set>
#include <exception>
#include <iostream>
namespace pt = boost::property_tree;

为了存储日志的配置信息，我们创建一个结构来存储它

struct debug_settings
{
    std::string m_file;               // log filename
    int m_level;                      // debug level
    std::set<std::string> m_modules;  // modules where logging is enabled
    void load(const std::string &filename);
    void save(const std::string &filename);
};

现在需要做的就是编写load()和save()成员函数的实现。让我们先来处理load()。它只包含7行代码，尽管它做了所有必要的事情，包括错误报告:

void debug_settings::load(const std::string &filename)
{
    // Create empty property tree object
    pt::ptree tree;

    // Parse the XML into the property tree.
    pt::read_xml(filename, tree);

    // Use the throwing version of get to find the debug filename.
    // If the path cannot be resolved, an exception is thrown.
    m_file = tree.get<std::string>("debug.filename");

    // Use the default-value version of get to find the debug level.
    // Note that the default value is used to deduce the target type.
    m_level = tree.get("debug.level", 0);

    // Use get_child to find the node containing the modules, and iterate over
    // its children. If the path cannot be resolved, get_child throws.
    // A C++11 for-range loop would also work.
    BOOST_FOREACH(pt::ptree::value_type &v, tree.get_child("debug.modules")) {
        // The data function is used to access the data stored in a node.
        m_modules.insert(v.second.data());
    }

}

存储函数

void debug_settings::save(const std::string &filename)
{
    // Create an empty property tree object.
    pt::ptree tree;

    // Put the simple values into the tree. The integer is automatically
    // converted to a string. Note that the "debug" node is automatically
    // created if it doesn‘t exist.
    tree.put("debug.filename", m_file);
    tree.put("debug.level", m_level);

    // Add all the modules. Unlike put, which overwrites existing nodes, add
    // adds a new node at the lowest level, so the "modules" node will have
    // multiple "module" children.
    BOOST_FOREACH(const std::string &name, m_modules)
        tree.add("debug.modules.module", name);

    // Write property tree to XML file
    pt::write_xml(filename, tree);
}

来个全代码的：

//
// Created by 瓜不甜 on 2018/1/20.
//
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/xml_parser.hpp>
#include <boost/foreach.hpp>
#include <string>
#include <set>
#include <exception>
#include <iostream>
namespace pt = boost::property_tree;

struct debug_settings
{
    std::string m_file;               // log filename
    int m_level;                      // debug level
    std::set<std::string> m_modules;  // modules where logging is enabled


    void load(const std::string &filename);
    void save(const std::string &filename);
};
void debug_settings::load(const std::string &filename)
{
    // Create empty property tree object
    pt::ptree tree;

    // Parse the XML into the property tree.
    pt::read_xml(filename, tree);

    // Use the throwing version of get to find the debug filename.
    // If the path cannot be resolved, an exception is thrown.
    m_file = tree.get<std::string>("debug.filename");

    // Use the default-value version of get to find the debug level.
    // Note that the default value is used to deduce the target type.
    m_level = tree.get("debug.level", 0);

    // Use get_child to find the node containing the modules, and iterate over
    // its children. If the path cannot be resolved, get_child throws.
    // A C++11 for-range loop would also work.
    BOOST_FOREACH(pt::ptree::value_type &v, tree.get_child("debug.modules")) {
                    // The data function is used to access the data stored in a node.
                    m_modules.insert(v.second.data());
                }

}

void debug_settings::save(const std::string &filename)
{
    // Create an empty property tree object.
    pt::ptree tree;

    // Put the simple values into the tree. The integer is automatically
    // converted to a string. Note that the "debug" node is automatically
    // created if it doesn‘t exist.
    tree.put("debug.filename", m_file);
    tree.put("debug.level", m_level);

    // Add all the modules. Unlike put, which overwrites existing nodes, add
    // adds a new node at the lowest level, so the "modules" node will have
    // multiple "module" children.
    BOOST_FOREACH(const std::string &name, m_modules)
                    tree.add("debug.modules.module", name);

    // Write property tree to XML file
    pt::write_xml(filename, tree);
}

void test1(){
    debug_settings a;
    a.load("setting.xml");
    std::cout<<a.m_file<<std::endl;
    std::cout<<a.m_level<<std::endl;
    std::set<std::string>::iterator i;
    for ( i = a.m_modules.begin(); i != a.m_modules.end(); ++i) {
        std::cout<<*i<<std::endl;
    }


}

很明显，这个是个非常好用的结构！

简单，高效！

这里有个foreach结构：

BOOST_FOREACH(const std::string &name, m_modules)

{

tree.add("debug.modules.module", name);

}

这个是C++的一个类宏的高级应用了

null

原文地址：https://www.cnblogs.com/xujintao/p/8325932.html