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json

来源：互联网 发布：淘宝购物发票怎么弄 编辑：程序博客网 时间：2024/06/16 17:39

JSON(JavaScript Object Notation)跟xml一样也是一种数据交换格式，了解json请参考其官网http://json.org/，本文不再对json做介绍，将重点介绍c++的json解析库的使用方法。json官网上列出了各种语言对应的json解析库，作者仅介绍自己使用过的两种C++的json解析库:jsoncpp(v0.5.0)和Boost(v1.34.0)。

因为要构造类似如下的

{"FurnitureItemObject":[],"FurniturePlaceItemObject":[],"RoomNum":0}

的json 数据，得用jsoncpp 构造一个空数组，在网上查了很久，自己也尝试了下，都没成功，没办法在群里向人请教，用resize 可以解决这个问题

[cpp] view plaincopy
  1. Json::Value root;  
  2. root["FurniturePlaceItemObject"].resize(0);  

就能构成空数组，记录下，供大家参考，也衷心希望与大家分享



 一. 使用jsoncpp解析json

Jsoncpp是个跨平台的开源库，首先从http://jsoncpp.sourceforge.net/上下载jsoncpp库源码，我下载的是v0.5.0，压缩包大约107K，解压，在jsoncpp-src-0.5.0/makefiles/vs71目录里找到jsoncpp.sln，用VS2003及以上版本编译，默认生成静态链接库。 在工程中引用，只需要include/json及.lib文件即可。

 使用JsonCpp前先来熟悉几个主要的类： 

Json::Value     可以表示里所有的类型，比如int,string,object,array等，具体应用将会在后边示例中介绍。

Json::Reader   将json文件流或字符串解析到Json::Value, 主要函数有Parse。

Json::Writer    与Json::Reader相反，将Json::Value转化成字符串流，注意它的两个子类：Json::FastWriter和Json::StyleWriter，分别输出不带格式的json和带格式的json。

 1. 从字符串解析json

  1. int ParseJsonFromString()  
  2. {  
  3.   const char* str = "{\"uploadid\": \"UP000000\",\"code\": 100,\"msg\": \"\",\"files\": \"\"}";  
  4.   
  5.   Json::Reader reader;  
  6.   Json::Value root;  
  7.   if (reader.parse(str, root))  // reader将Json字符串解析到root，root将包含Json里所有子元素   
  8.   {  
  9.     std::string upload_id = root["uploadid"].asString();  // 访问节点，upload_id = "UP000000"   
  10.     int code = root["code"].asInt();    // 访问节点，code = 100   
  11.   }  
  12.   return 0;  
  13. }  
</pre><p style="font-size:13px; line-height:19.5px; margin:10px auto; font-family:Verdana,Geneva,Arial,Helvetica,sans-serif"><span style="line-height:1.5">2. 从文件解析json</span></p><p style="font-size:13px; line-height:19.5px; margin:10px auto; font-family:Verdana,Geneva,Arial,Helvetica,sans-serif"><span style="line-height:1.5">json文件内容：</span></p><div class="dp-highlighter bg_cpp" style="font-family:Consolas,'Courier New',Courier,mono,serif; overflow:auto; word-break:break-word; margin:18px 0px!important"><ol class="dp-cpp" style="padding-left:40px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; padding-top:0px!important; padding-right:0px!important; padding-bottom:0px!important"><li class="alt" style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; color:inherit; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">{  </span></li><li style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">    </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"uploadid"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">: </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"UP000000"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">,  </span></li><li class="alt" style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; color:inherit; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">    </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"code"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">: </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"0"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">,  </span></li><li style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">    </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"msg"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">: </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">""</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">,  </span></li><li class="alt" style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; color:inherit; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">    </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"files"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">:  </span></li><li style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">    [  </span></li><li class="alt" style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; color:inherit; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">        {  </span></li><li style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">            </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"code"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">: </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"0"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">,  </span></li><li class="alt" style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; color:inherit; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">            </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"msg"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">: </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">""</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">,  </span></li><li style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">            </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"filename"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">: </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"1D_16-35_1.jpg"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">,  </span></li><li class="alt" style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; color:inherit; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">            </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"filesize"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">: </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"196690"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">,  </span></li><li style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">            </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"width"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">: </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"1024"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">,  </span></li><li class="alt" style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; color:inherit; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">            </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"height"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">: </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"682"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">,  </span></li><li style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">            </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"images"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">:  </span></li><li class="alt" style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; color:inherit; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">            [  </span></li><li style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">                {  </span></li><li class="alt" style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; color:inherit; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">                    </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"url"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">: </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"fmn061/20111118"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">,  </span></li><li style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">                    </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"type"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">: </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"large"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">,  </span></li><li class="alt" style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; color:inherit; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">                    </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"width"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">: </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"720"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">,  </span></li><li style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">                    </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"height"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">: </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"479"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">  </span></li><li class="alt" style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; color:inherit; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">                },  </span></li><li style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">                {  </span></li><li class="alt" style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; color:inherit; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">                    </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"url"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">: </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"fmn061/20111118"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">,  </span></li><li style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">                    </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"type"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">: </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"main"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">,  </span></li><li class="alt" style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; color:inherit; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">                    </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"width"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">: </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"200"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">,  </span></li><li style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">                    </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"height"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">: </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"133"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">  </span></li><li class="alt" style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; color:inherit; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">                }  </span></li><li style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">            ]  </span></li><li class="alt" style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; color:inherit; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">        }  </span></li><li style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">    ]  </span></li><li class="alt" style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; color:inherit; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">}  </span></li></ol></div><pre code_snippet_id="1550873" snippet_file_name="blog_20160107_2_5762465" name="code" class="cpp" style="margin-top: 0px; margin-bottom: 0px; white-space: pre-wrap; word-wrap: break-word; font-size: 13px; line-height: 19.5px; background-color: rgb(255, 255, 255);">

 解析代码：

  1. int ParseJsonFromFile(const char* filename)  
  2. {  
  3.   // 解析json用Json::Reader   
  4.   Json::Reader reader;  
  5.   // Json::Value是一种很重要的类型，可以代表任意类型。如int, string, object, array...   
  6.   Json::Value root;         
  7.   
  8.   std::ifstream is;  
  9.   is.open (filename, std::ios::binary );    
  10.   if (reader.parse(is, root))  
  11.   {  
  12.     std::string code;  
  13.     if (!root["files"].isNull())  // 访问节点，Access an object value by name, create a null member if it does not exist.   
  14.       code = root["uploadid"].asString();  
  15.       
  16.     // 访问节点，Return the member named key if it exist, defaultValue otherwise.   
  17.     code = root.get("uploadid", "null").asString();  
  18.   
  19.     // 得到"files"的数组个数   
  20.     int file_size = root["files"].size();  
  21.   
  22.     // 遍历数组   
  23.     for(int i = 0; i < file_size; ++i)  
  24.     {  
  25.       Json::Value val_image = root["files"][i]["images"];  
  26.       int image_size = val_image.size();  
  27.       for(int j = 0; j < image_size; ++j)  
  28.       {  
  29.         std::string type = val_image[j]["type"].asString();  
  30.         std::string url = val_image[j]["url"].asString();  
  31.       }  
  32.     }  
  33.   }  
  34.   is.close();  
  35.   return 0;  
  36. }  
</pre><p style="font-size:13px; line-height:19.5px; margin:10px auto; font-family:Verdana,Geneva,Arial,Helvetica,sans-serif"><span style="line-height:1.5"> 3. 在json结构中插入json</span></p><div class="dp-highlighter bg_cpp" style="font-family:Consolas,'Courier New',Courier,mono,serif; overflow:auto; word-break:break-word; margin:18px 0px!important"><ol class="dp-cpp" style="padding-left:40px; border:none; color:rgb(92,92,92); margin:0px 0px 1px 45px!important; padding-top:0px!important; padding-right:0px!important; padding-bottom:0px!important"><li class="alt" style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; color:inherit; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">Json::Value arrayObj;   </span><span class="comment" style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,130,0); background-color:inherit">// 构建对象 </span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">  </span></li><li style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">Json::Value new_item, new_item1;  </span></li><li class="alt" style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; color:inherit; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">new_item[</span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"date"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">] = </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"2011-12-28"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">;  </span></li><li style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">new_item1[</span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"time"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">] = </span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"22:30:36"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">;  </span></li><li class="alt" style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; color:inherit; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">arrayObj.append(new_item);  </span><span class="comment" style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,130,0); background-color:inherit">// 插入数组成员 </span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">  </span></li><li style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">arrayObj.append(new_item1); </span><span class="comment" style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,130,0); background-color:inherit">// 插入数组成员 </span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">  </span></li><li class="alt" style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; color:inherit; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important"><span class="datatypes" style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">int</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit"> file_size = root[</span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"files"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">].size();  </span></li><li style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important; background-color:rgb(248,248,248)"><span class="keyword" style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,102,153); font-weight:bold; background-color:inherit">for</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">(</span><span class="datatypes" style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">int</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit"> i = 0; i < file_size; ++i)  </span></li><li class="alt" style="border-style:none none none solid; border-left-width:3px; border-left-color:rgb(108,226,108); list-style:decimal outside; color:inherit; line-height:1.6; margin:0px!important; padding:0px 3px 0px 10px!important"><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">  root[</span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"files"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">][i][</span><span class="string" style="line-height:1.5; margin:0px; padding:0px; border:none; color:blue; background-color:inherit">"exifs"</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">] = arrayObj;   </span><span class="comment" style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,130,0); background-color:inherit">// 插入原json中</span><span style="line-height:1.5; margin:0px; padding:0px; border:none; color:rgb(0,0,0); background-color:inherit">  </span></li></ol></div><pre code_snippet_id="1550873" snippet_file_name="blog_20160107_4_5794702" name="code" class="cpp" style="margin-top: 0px; margin-bottom: 0px; white-space: pre-wrap; word-wrap: break-word; font-size: 13px; line-height: 19.5px; background-color: rgb(255, 255, 255);"><span style="color: rgb(255, 0, 0); font-family: Arial; font-size: 14px; line-height: 26px;">if (root["url"].type() != Json::nullValue) 检测是否存在</span>

 4. 输出json

  1. // 转换为字符串（带格式）   
  2. std::string out = root.toStyledString();  
  3. // 输出无格式json字符串   
  4. Json::FastWriter writer;  
  5. std::string out2 = writer.write(root);  
// 转换为字符串（带格式）std::string out = root.toStyledString();// 输出无格式json字符串Json::FastWriter writer;std::string out2 = writer.write(root);

二. 使用Boost property_tree解析json

property_tree可以解析xml，json，ini，info等格式的数据，用property_tree解析这几种格式使用方法很相似。

解析json很简单，命名空间为boost::property_tree，reson_json函数将文件流、字符串解析到ptree，write_json将ptree输出为字符串或文件流。其余的都是对ptree的操作。

解析json需要加头文件：

#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>

1. 解析json

解析一段下面的数据：

  1. {  
  2.   "code": 0,  
  3.   "images":  
  4.   [  
  5.     {  
  6.       "url": "fmn057/20111221/1130/head_kJoO_05d9000251de125c.jpg"  
  7.     },  
  8.     {  
  9.       "url": "fmn057/20111221/1130/original_kJoO_05d9000251de125c.jpg"  
  10.     }  
  11.   ]  
  12. }  
{  "code": 0,  "images":  [    {      "url": "fmn057/20111221/1130/head_kJoO_05d9000251de125c.jpg"    },    {      "url": "fmn057/20111221/1130/original_kJoO_05d9000251de125c.jpg"    }  ]}
  1. int ParseJson()  
  2. {  
  3.   std::string str = "{\"code\":0,\"images\":[{\"url\":\"fmn057/20111221/1130/head_kJoO_05d9000251de125c.jpg\"},{\"url\":\"fmn057/20111221/1130/original_kJoO_05d9000251de125c.jpg\"}]}";  
  4.   using namespace boost::property_tree;  
  5.   
  6.   std::stringstream ss(str);  
  7.   ptree pt;  
  8.   try{      
  9.     read_json(ss, pt);  
  10.   }  
  11.   catch(ptree_error & e) {  
  12.     return 1;   
  13.   }  
  14.   
  15.   try{  
  16.     int code = pt.get<int>("code");   // 得到"code"的value   
  17.     ptree image_array = pt.get_child("images");  // get_child得到数组对象   
  18.       
  19.     // 遍历数组   
  20.     BOOST_FOREACH(boost::property_tree::ptree::value_type &v, image_array)  
  21.     {  
  22.       std::stringstream s;  
  23.       write_json(s, v.second);  
  24.       std::string image_item = s.str();  
  25.     }  
  26.   }  
  27.   catch (ptree_error & e)  
  28.   {  
  29.     return 2;  
  30.   }  
  31.   return 0;  
  32. }  
int ParseJson(){  std::string str = "{\"code\":0,\"images\":[{\"url\":\"fmn057/20111221/1130/head_kJoO_05d9000251de125c.jpg\"},{\"url\":\"fmn057/20111221/1130/original_kJoO_05d9000251de125c.jpg\"}]}";  using namespace boost::property_tree;  std::stringstream ss(str);  ptree pt;  try{        read_json(ss, pt);  }  catch(ptree_error & e) {    return 1;   }  try{    int code = pt.get<int>("code");   // 得到"code"的value    ptree image_array = pt.get_child("images");  // get_child得到数组对象        // 遍历数组    BOOST_FOREACH(boost::property_tree::ptree::value_type &v, image_array)    {      std::stringstream s;      write_json(s, v.second);      std::string image_item = s.str();    }  }  catch (ptree_error & e)  {    return 2;  }  return 0;}

2. 构造json

  1. int InsertJson()  
  2. {  
  3.   std::string str = "{\"code\":0,\"images\":[{\"url\":\"fmn057/20111221/1130/head_kJoO_05d9000251de125c.jpg\"},{\"url\":\"fmn057/20111221/1130/original_kJoO_05d9000251de125c.jpg\"}]}";  
  4.   using namespace boost::property_tree;  
  5.   
  6.   std::stringstream ss(str);  
  7.   ptree pt;  
  8.   try{      
  9.     read_json(ss, pt);  
  10.   }  
  11.   catch(ptree_error & e) {  
  12.     return 1;   
  13.   }  
  14.   
  15.   // 修改/增加一个key-value，key不存在则增加   
  16.   pt.put("upid", "00001");  
  17.   
  18.   // 插入一个数组   
  19.   ptree exif_array;  
  20.   ptree array1, array2, array3;  
  21.   array1.put("Make", "NIKON");  
  22.   array2.put("DateTime", "2011:05:31 06:47:09");  
  23.   array3.put("Software", "Ver.1.01");  
  24.   exif_array.push_back(std::make_pair("", array1));  
  25.   exif_array.push_back(std::make_pair("", array2));  
  26.   exif_array.push_back(std::make_pair("", array3));  
  27.   
  28. //   exif_array.push_back(std::make_pair("Make", "NIKON"));   
  29. //   exif_array.push_back(std::make_pair("DateTime", "2011:05:31 06:47:09"));   
  30. //   exif_array.push_back(std::make_pair("Software", "Ver.1.01"));   
  31.   
  32.   pt.put_child("exifs", exif_array);  
  33.   std::stringstream s2;  
  34.   write_json(s2, pt);  
  35.   std::string outstr = s2.str();  
  36.   
  37.   return 0;  
  38. }  
int InsertJson(){  std::string str = "{\"code\":0,\"images\":[{\"url\":\"fmn057/20111221/1130/head_kJoO_05d9000251de125c.jpg\"},{\"url\":\"fmn057/20111221/1130/original_kJoO_05d9000251de125c.jpg\"}]}";  using namespace boost::property_tree;  std::stringstream ss(str);  ptree pt;  try{        read_json(ss, pt);  }  catch(ptree_error & e) {    return 1;   }  // 修改/增加一个key-value，key不存在则增加  pt.put("upid", "00001");  // 插入一个数组  ptree exif_array;  ptree array1, array2, array3;  array1.put("Make", "NIKON");  array2.put("DateTime", "2011:05:31 06:47:09");  array3.put("Software", "Ver.1.01");  exif_array.push_back(std::make_pair("", array1));  exif_array.push_back(std::make_pair("", array2));  exif_array.push_back(std::make_pair("", array3));//   exif_array.push_back(std::make_pair("Make", "NIKON"));//   exif_array.push_back(std::make_pair("DateTime", "2011:05:31 06:47:09"));//   exif_array.push_back(std::make_pair("Software", "Ver.1.01"));  pt.put_child("exifs", exif_array);  std::stringstream s2;  write_json(s2, pt);  std::string outstr = s2.str();  return 0;}

 

三. 两种解析库的使用经验

1. 用boost::property_tree解析字符串遇到"\/"时解析失败，而jsoncpp可以解析成功，要知道'/'前面加一个'\'是JSON标准格式。

2. boost::property_tree的read_json和write_json在多线程中使用会引起崩溃。

针对1，可以在使用boost::property_tree解析前写个函数去掉"\/"中的'\'，针对2，在多线程中同步一下可以解决。

我的使用心得：使用boost::property_tree不仅可以解析json，还可以解析xml，info等格式的数据。对于解析json，使用boost::property_tree解析还可以忍受，但解析xml，由于遇到问题太多只能换其它库了。

 

from：http://blog.csdn.net/hzyong

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