如何选择JSON

Question

这里JSON值

{"ts":1827908701,"updates":[[4,30623409,17,81282347579,1425823449632," ... ","tfs"],[80,1,0],[7,81282347579,30652308]]} 

我怎样才能使用图书馆升压更新的价值4？

我知道如何取这样的“ts”值。但我不知道如何把两个支架

Answer 1

技术上的价值，这样的回答显示了如何使用频加速至提取值：

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#include <boost/fusion/adapted/std_pair.hpp> 
#include <boost/spirit/include/qi.hpp> 
#include <boost/spirit/include/phoenix.hpp> 
#include <map> 

namespace qi = boost::spirit::qi; 

std::string const sample = R"({"ts":1827908701,"updates":[[4,30623409,17,81282347579,1425823449632," ... ","tfs"],[80,1,0],[7,81282347579,30652308]]})"; 

namespace qd_json { // quick and dirty JSON handling 
    struct null {}; 
    using text = std::string; 
    using value = boost::make_recursive_variant< 
      null, 
      text,          // "string" (roughly!) 
      double,         // number 
      std::map<text, boost::recursive_variant_>, // object 
      std::vector<boost::recursive_variant_>, // array 
      bool 
     >::type; 
    using member = std::pair<text, value>; 
    using object = std::map<text, value>; 
    using array = std::vector<value>; 

    template <typename It, typename Skipper = qi::space_type> 
    struct grammar : qi::grammar<It, value(), Skipper> 
    { 
     grammar() : grammar::base_type(value_) { 
      using namespace qi; 

      text_ = '"' >> raw [*('\\' >> char_ | ~char_('"'))] >> '"'; 
      null_ = "null" >> attr(null{}); 
      bool_ = "true" >> attr(true) | "false" >> attr(false); 
      value_ = null_ | bool_ | text_ | double_ | object_ | array_; 
      member_ = text_ >> ':' >> value_; 
      object_ = '{' >> -(member_ % ',') >> '}'; 
      array_ = '[' >> -(value_ % ',') >> ']'; 

      //////////////////////////////////////// 
      // Bonus: properly decoding the string: 
      text_ = lexeme [ '"' >> *ch_ >> '"' ]; 

      ch_ = +(
        ~char_("\"\\")) [ _val += _1 ] | 
         qi::lit("\x5C") >> (    // \ (reverse solidus) 
         qi::lit("\x22") [ _val += '"' ] | // " quotation mark U+0022 
         qi::lit("\x5C") [ _val += '\\' ] | // \ reverse solidus U+005C 
         qi::lit("\x2F") [ _val += '/' ] | /// solidus   U+002F 
         qi::lit("\x62") [ _val += '\b' ] | // b backspace  U+0008 
         qi::lit("\x66") [ _val += '\f' ] | // f form feed  U+000C 
         qi::lit("\x6E") [ _val += '\n' ] | // n line feed  U+000A 
         qi::lit("\x72") [ _val += '\r' ] | // r carriage return U+000D 
         qi::lit("\x74") [ _val += '\t' ] | // t tab    U+0009 
         qi::lit("\x75")     // uXXXX    U+XXXX 
          >> _4HEXDIG [ append_utf8(qi::_val, qi::_1) ] 
        ); 

      BOOST_SPIRIT_DEBUG_NODES((text_)(value_)(member_)(object_)(array_)(null_)(bool_)) 
     } 
    private: 
     qi::rule<It, text()>   text_, ch_; 
     qi::rule<It, null()>   null_; 
     qi::rule<It, bool()>   bool_; 
     qi::rule<It, value(), Skipper> value_; 
     qi::rule<It, member(), Skipper> member_; 
     qi::rule<It, object(), Skipper> object_; 
     qi::rule<It, array(), Skipper> array_; 

     struct append_utf8_f { 
      template <typename...> struct result { typedef void type; }; 
      template <typename String, typename Codepoint> 
      void operator()(String& to, Codepoint codepoint) const { 
       auto out = std::back_inserter(to); 
       boost::utf8_output_iterator<decltype(out)> convert(out); 
       *convert++ = codepoint; 
      } 
     }; 
     boost::phoenix::function<append_utf8_f> append_utf8; 
     qi::uint_parser<uint32_t, 16, 4, 4> _4HEXDIG; 
    }; 

    template <typename Range, typename It = typename boost::range_iterator<Range const>::type> 
    value parse(Range const& input) { 
     grammar<It> g; 

     It first(boost::begin(input)), last(boost::end(input)); 
     value parsed; 
     bool ok = qi::phrase_parse(first, last, g, qi::space, parsed); 

     if (ok && (first == last)) 
      return parsed; 

     throw std::runtime_error("Remaining unparsed: '" + std::string(first, last) + "'"); 
    } 

    namespace accessors { 
     static double   dbl_(qd_json::value const&v) { return boost::get<double>(v); } 
     static int    int_(qd_json::value const&v) { return boost::get<double>(v); } 
     static std::string  txt_(qd_json::value const&v) { return boost::get<qd_json::text>(v); } 
     static qd_json::array arr_(qd_json::value const&v) { return boost::get<qd_json::array>(v); } 
     static qd_json::object obj_(qd_json::value const&v) { return boost::get<qd_json::object>(v); } 
    } 
} 

using It = std::string::const_iterator; 

int main() 
{ 
    using namespace qd_json::accessors; 

    auto root = obj_(qd_json::parse(sample)); 

    for(auto& updates : arr_(root["updates"])) 
     for(auto& first : arr_(updates)) 
     { 
      std::cout << int_(first) << "\n"; 
      return 0; 
     } 
} 

打印：

4 

解析器当然是礼貌的旧答案（Getting values from a json file using boost/property_tree, with multiple elements/arrays/sub-arrays C++），如果你需要更具体的答案，我建议你展示你已经得到的代码。