libconfig C++ 学习笔记

1. C++API 头文件 #include <libconfig.h++> ，命名空间：using namespace libconfig;

2.多线程使用问题：

　　（1）libconfig是完全可重入的,库中函数不使用全局变量和不保持成功调用间的状态。所以两个独立配置文件在两个不同线程间并发操作可以是安全的；

　　（2）libconfig是线程不安全，libconfig不考虑系统线程模型。所以一个配置文件的实例被多个线程获取，必须使用同步机制（例如读写锁或互斥锁）来保护。

　　（3）libconfig不是异步安全，不能在信号句柄中调用

　　（4）libconfig不能保证取消安全。因为它不知道主机系统的线程模型，库不包含任何线程取消点。在大多数情况下这将不是多线程程序的问题。但是，请注意一些库中的例程（即那些从/到文件读取/写入配置的程序）流）使用可能会阻止的C库例程执行I/O；是否这些C库例程是取消安全的，取决于主机系统。

3.C++API

　　C++API使用Config类和Setting类，因为不提供公有的copy constructor or assignment operator，所以在函数参数中传递时使用引用或指针方式
4.使用方法（使用官方example）：

配置文件：

// An example configuration file that stores information about a store.

// Basic store information:
name = "Books, Movies & More";

// Store inventory:
inventory =
{
  books = ( { title  = "Treasure Island";
              author = "Robert Louis Stevenson";
              price  = 29.99;
              qty    = 5; },
            { title  = "Snow Crash";
              author = "Neal Stephenson";
              price  = 9.99;
              qty    = 8; }
          );

  movies = ( { title = "Brazil";
               media = "DVD";
               price = 19.99;
               qty = 11; },
             { title = "The City of Lost Children";
               media = "DVD";
               price = 18.99;
               qty = 5; },
             { title = "Memento";
               media = "Blu-Ray";
               price = 24.99;
               qty = 20;
             },
             { title = "Howard the Duck"; }
           );
};

// Store hours:
hours =
{
  mon = { open =  9; close = 18; };
  tue = { open =  9; close = 18; };
  wed = { open =  9; close = 18; };
  thu = { open =  9; close = 18; };
  fri = { open =  9; close = 20; };
  sat = { open =  9; close = 20; };
  sun = { open = 11; close = 16; };
};

C++读取配置程序：

#include <cstdlib>
#include <libconfig.h++>
#include <iostream>
#include <iomanip>

using namespace std;
using namespace libconfig;

int main(){
    Config cfg;     //1.声明 Config对象

    cfg.readFile("example.cfg");    //读取配置文件

    // Get the store name.
    try
    {
        string name = cfg.lookup("name");
        cout << "Store name: " << name << endl << endl;
    }
    catch(const SettingNotFoundException &nfex)         //配置没找到会有SettingNotFoundException 异常
    {
        cerr << "No 'name' setting in configuration file." << endl;
    }
    // Get the store name.
  try
  {
    string name = cfg.lookup("name");
    cout << "Store name: " << name << endl << endl;
  }
  catch(const SettingNotFoundException &nfex)
  {
    cerr << "No 'name' setting in configuration file." << endl;
  }

  const Setting& root = cfg.getRoot();

  // Output a list of all books in the inventory.
  try
  {
    const Setting &books = root["inventory"]["books"];
    int count = books.getLength();

    cout << setw(30) << left << "TITLE" << "  "
         << setw(30) << left << "AUTHOR" << "   "
         << setw(6) << left << "PRICE" << "  "
         << "QTY"
         << endl;

    for(int i = 0; i < count; ++i)
    {
      const Setting &book = books[i];

      // Only output the record if all of the expected fields are present.
      string title, author;
      double price;
      int qty;

      if(!(book.lookupValue("title", title)
           && book.lookupValue("author", author)
           && book.lookupValue("price", price)
           && book.lookupValue("qty", qty)))
        continue;

      cout << setw(30) << left << title << "  "
           << setw(30) << left << author << "  "
           << '$' << setw(6) << right << price << "  "
           << qty
           << endl;
    }
    cout << endl;
  }
  catch(const SettingNotFoundException &nfex)
  {
    // Ignore.
  }

  // Output a list of all books in the inventory.
  try
  {
    const Setting &movies = root["inventory"]["movies"];
    int count = movies.getLength();

    cout << setw(30) << left << "TITLE" << "  "
         << setw(10) << left << "MEDIA" << "   "
         << setw(6) << left << "PRICE" << "  "
         << "QTY"
         << endl;

    for(int i = 0; i < count; ++i)
    {
      const Setting &movie = movies[i];

      // Only output the record if all of the expected fields are present.
      string title, media;
      double price;
      int qty;

      if(!(movie.lookupValue("title", title)
           && movie.lookupValue("media", media)
           && movie.lookupValue("price", price)
           && movie.lookupValue("qty", qty)))
        continue;

      cout << setw(30) << left << title << "  "
           << setw(10) << left << media << "  "
           << '$' << setw(6) << right << price << "  "
           << qty
           << endl;
    }
    cout << endl;
  }
  catch(const SettingNotFoundException &nfex)
  {
    // Ignore.
  }
    return 0;
}

5.常用Config类方法：

（1）Method on Config: Setting & getRoot () const

This method returns the root setting for the configuration, which is a group.

（2）

Method on Config: Setting & lookup (const std::string &path) constMethod on Config: Setting & lookup (const char * path) const

These methods locate the setting specified by the path path. If the requested setting is not found, a SettingNotFoundException is thrown.

（3）

Method on Config: bool lookupValue (const char *path, bool &value) constMethod on Config: bool lookupValue (const std::string &path, bool &value) constMethod on Config: bool lookupValue (const char *path, int &value) constMethod on Config: bool lookupValue (const std::string &path, int &value) constMethod on Config: bool lookupValue (const char *path, unsigned int &value) constMethod on Config: bool lookupValue (const std::string &path, unsigned int &value) constMethod on Config: bool lookupValue (const char *path, long long &value) constMethod on Config: bool lookupValue (const std::string &path, long long &value) constMethod on Config: bool lookupValue (const char *path, float &value) constMethod on Config: bool lookupValue (const std::string &path, float &value) constMethod on Config: bool lookupValue (const char *path, double &value) constMethod on Config: bool lookupValue (const std::string &path, double &value) constMethod on Config: bool lookupValue (const char *path, const char *&value) constMethod on Config: bool lookupValue (const std::string &path, const char *&value) constMethod on Config: bool lookupValue (const char *path, std::string &value) constMethod on Config: bool lookupValue (const std::string &path, std::string &value) const