由于另一个答案中的数据结构被认为“非常复杂”，因此建议目标数据结构为：
struct Data { struct Folder { int id, parent_id; std::string path; }; struct File { int id, parent_id; std::string path, name, md5_hash; }; using Folders = std::vector<Folder>; using Files = std::vector<File>; Folders folders; Files files;};但是，如果我们“跳过中间人”并将JSON专门解析为所示
Data结构，则OP可能会更满意。这“简化”了语法，使其仅针对此类文档：
start = '{' >> (folders_ >> commasep) ^(files_ >> commasep) >> '}';folders_ = prop_key(+"folders") >> '[' >> -(folder_ % ',') >> ']';files_ = prop_key(+"files") >> '[' >> -(file_ % ',') >> ']';folder_ = '{' >> ( (prop_key(+"id") >> int_ >> commasep) ^ (prop_key(+"parent_id") >> int_ >> commasep) ^ (prop_key(+"path") >> text_ >> commasep) ) >> '}';file_ = '{' >> ( (prop_key(+"id") >> int_ >> commasep) ^ (prop_key(+"parent_id") >> int_ >> commasep) ^ (prop_key(+"path") >> text_ >> commasep) ^ (prop_key(+"name") >> text_ >> commasep) ^ (prop_key(+"hash") >> text_ >> commasep) ) >> '}';prop_key = lexeme ['"' >> lazy(_r1) >> '"'] >> ':';commasep = &char_('}') | ',';这个语法允许
- 无关紧要的空格，
- 对象内属性的重新排序
- 和省略的对象属性
优点：
- 及早检查属性值类型
- 缩短编译时间
- 确实减少了代码： 减少了37个LoC （不计算样本JSON行的〜22％）
最后一个好处是反面：如果您想读取稍有不同的JSON，现在您需要处理语法，而不仅仅是编写其他提取/转换。
在37行代码中，我偏爱其他答案，但我将由您自己决定。
这是直接使用此语法的相同演示程序：
[Live On Coliru](http://coliru.stacked-crooked.com/a/cbbe576146a96f58)
//#define BOOST_SPIRIT_DEBUG#include <boost/fusion/adapted.hpp>#include <boost/spirit/include/qi.hpp>#include <boost/spirit/include/phoenix.hpp>namespace qi = boost::spirit::qi;static std::string const sample = R"( { "folders" : [{ "id" : 109, "parent_id" : 110, "path" : "/1/105/110/" }, { "id" : 110, "parent_id" : 105, "path" : "/1/105/" } ], "files" : [{ "id" : 26, "parent_id" : 105, "name" : "picture.png", "hash" : "md5_hash", "path" : "/1/105/" }, { "id" : 25, "parent_id" : 110, "name" : "another_picture.jpg", "hash" : "md5_hash", "path" : "/1/105/110/" } ] })";struct Data { struct Folder { int id, parent_id; std::string path; }; struct File { int id, parent_id; std::string path, name, md5_hash; }; using Folders = std::vector<Folder>; using Files = std::vector<File>; Folders folders; Files files;};BOOST_FUSION_ADAPT_STRUCT(data::Folder, (int,id)(int,parent_id)(std::string,path))BOOST_FUSION_ADAPT_STRUCT(data::File, (int,id)(int,parent_id)(std::string,path)(std::string,name)(std::string,md5_hash))BOOST_FUSION_ADAPT_STRUCT(Data, (data::Folders,folders)(data::Files,files))namespace folder_info { // adhoc JSON parser template <typename It, typename Skipper = qi::space_type> struct grammar : qi::grammar<It, Data(), Skipper> { grammar() : grammar::base_type(start) { using namespace qi; start = '{' >> (folders_ >> commasep) ^ (files_ >> commasep) >> '}'; folders_ = prop_key(+"folders") >> '[' >> -(folder_ % ',') >> ']'; files_ = prop_key(+"files") >> '[' >> -(file_ % ',') >> ']'; folder_ = '{' >> ( (prop_key(+"id") >> int_ >> commasep) ^ (prop_key(+"parent_id") >> int_ >> commasep) ^ (prop_key(+"path") >> text_ >> commasep) ) >> '}'; file_ = '{' >> ( (prop_key(+"id") >> int_ >> commasep) ^ (prop_key(+"parent_id") >> int_ >> commasep) ^ (prop_key(+"path") >> text_ >> commasep) ^ (prop_key(+"name") >> text_ >> commasep) ^ (prop_key(+"hash") >> text_ >> commasep) ) >> '}'; prop_key = lexeme ['"' >> lazy(_r1) >> '"'] >> ':'; commasep = &char_('}') | ','; //////////////////////////////////////// // Bonus: properly decoding the string: text_ = '"' >> *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((files_)(folders_)(file_)(folder_)(start)(text_)) } private: qi::rule<It, Data(), Skipper> start; qi::rule<It, data::Files(), Skipper> files_; qi::rule<It, data::Folders(), Skipper> folders_; qi::rule<It, data::File(), Skipper> file_; qi::rule<It, data::Folder(), Skipper> folder_; qi::rule<It, void(const char*), Skipper> prop_key; qi::rule<It, std::string()> text_, ch_; qi::rule<It> commasep; struct append_utf8_f { template <typename...> struct result { typedef void type; }; template <typename String, typename Codepoint> void operator()(String& to, Codepoint prepoint) const { auto out = std::back_inserter(to); boost::utf8_output_iterator<decltype(out)> convert(out); *convert++ = prepoint; } }; 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> Data parse(Range const& input) { grammar<It> g; It first(boost::begin(input)), last(boost::end(input)); Data 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) + "'"); }}int main(){ auto parsed = folder_info::parse(sample); for (auto& e : parsed.folders) std::cout << "folder:t" << e.id << "t" << e.path << "n"; for (auto& e : parsed.files) std::cout << "file:t" << e.id << "t" << e.path << "t" << e.name << "n";}输出：
folder: 109 /1/105/110/folder: 110 /1/105/file: 26 /1/105/ picture.pngfile: 25 /1/105/110/ another_picture.jpg
