HTTP服务器向我发送一个JSON响应（字符串），如下所示：
{
"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\/"
}
]
}
我想比较一个远程文件夹＆＃34;树＃34;使用本地文件夹树（例如包含我本地文件位置的字符串向量），所以我想在地图上转换这个JSON（字符串，矢量（地图（字符串，字符串）））（我不要这样做）知道这是否可行。）
我正在开发一个工具来同步本地和远程文件夹之间的文件，所以我使用boost来列出本地文件夹，我想将本地列表与远程列表进行比较（ JSON响应）生成操作（下载本地文件夹中不存在的丢失文件，上传远程文件夹中不存在的文件）。
使用此功能我在另一个问题上找到了：
void print(boost::property_tree::ptree const& pt)
{
using boost::property_tree::ptree;
ptree::const_iterator end = pt.end();
for (ptree::const_iterator it = pt.begin(); it != end; ++it)
{
std::cout << it->first << ": " << it->second.get_value<std::string>() << std::endl;
print(it->second);
}
}
我成功地打印了这样的东西：
folders:
:
id: 109
parent_id: 110
name: 2011_pictures
:
id: 110
parent_id: 105
name: Aminos
files:
id: 26
parent_id: 105
name: logo.png
:
id: 5
parent_id: 109
name: me.jpg
我想知道是否可以使用此结果生成map<string, vector <map<string,string> > >，它将有2个键：＆＃34;文件夹＆＃34;和＆＃34;文件＆＃34;使用这两个键，我们可以访问包含每个对象（文件或文件夹）信息的类型映射的向量。如果这是可行的，它将降低任务的复杂性（比较两个文件夹列表）
示例：T [＆＃34;文件夹＆＃34;] [0] [＆＃34; id＆＃34;]将返回＆＃34; 109＆＃34; ; T [＆＃34; files＆＃34;] [0] [＆＃34; name＆＃34;]将返回＆＃34; logo.png＆＃34;
更新：这个问题已经过时但我想提出一个建议：每当你想在C ++下处理Json时都要使用RAPIDJSON。
答案 0 :(得分：2)
免责声明：以下示例不是一个完整的JSON解析器。考虑使用支持您需求的库。您可以在此处查看更加进化的JSON解析器https://github.com/sehe/spirit-v2-json
快速而肮脏的精神语法（假设你不需要太多的一致性）将是：
text_ = '"' >> raw [*('\\' >> char_ | ~char_('"'))] >> '"'; // ¹
value_ = null | bool | text_ | double_ | object_ | array_; // ²
member_ = text_ >> ':' >> value_;
object_ = '{' >> -(member_ % ',') >> '}';
array_ = '[' >> -(value_ % ',') >> ']';
// ¹ as a bonus I added utf8 escape decoding in the full sample
// ² as another bonus I threw in the missing `null` and `bool` types
使用AST进行转换为C ++类型而无需进一步努力：
using text = std::string;
using value = boost::make_recursive_variant<
null,
bool,
text, // "string" (roughly!)
double, // number
std::map<text, boost::recursive_variant_>, // object
std::vector<boost::recursive_variant_> // array
>::type;
using member = std::pair<text, value>;
using object = std::map<text, value>;
using array = std::vector<value>;
如果你有两个qd_json::value个对象，你可以比较它们：
qd_json::value local_tree, remote_tree;
if (local_tree == remote_tree)
{
std::cout << "the tree is unchanged\n";
}
这是一个演示程序：
演示已更新，向您展示如何进入＆＃34;用户友好型＆＃34;您在编辑问题时建议的数据结构：
int main() {
auto json = qd_json::parse(sample);
// extract into user friendly datastructure from the question:
auto extracted = Data::extract_from(json);
for (auto& e : extracted.folders) std::cout << "folder:\t" << e.id << "\t" << e.path << "\n";
for (auto& e : extracted.files) std::cout << "file:\t" << e.id << "\t" << e.path << "\t" << e.name << "\n";
}
<强> Live On Coliru
#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;
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\/"
}
]
})";
namespace qd_json { // quick and dirty JSON handling
struct null {
bool operator==(null) const { return true; }
};
inline static std::ostream& operator<<(std::ostream& os, null) { return os << "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) + "'");
}
}
#include <boost/range/algorithm.hpp>
#include <boost/range/adaptors.hpp>
#include <boost/range/algorithm_ext/push_back.hpp>
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;
static Data extract_from(qd_json::value const& json) {
using namespace boost::adaptors;
return {
boost::copy_range<Folders>(arr(obj(json).at("folders")) | transformed(obj) | transformed(&Data::extract_folder)),
boost::copy_range<Files> (arr(obj(json).at("files")) | transformed(obj) | transformed(&Data::extract_file)),
};
}
private:
static Folder extract_folder(qd_json::object const& obj) {
return {
id (obj.at("id")),
id (obj.at("parent_id")),
text (obj.at("path"))
};
}
static File extract_file(qd_json::object const& obj) {
return {
id (obj.at("id")),
id (obj.at("parent_id")),
text (obj.at("path")),
text (obj.at("name")),
text (obj.at("hash")),
};
}
static int id (qd_json::value const&v) { return boost::get<double>(v); };
static std::string text(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); };
};
int main()
{
auto json = qd_json::parse(sample);
// compare json documents
qd_json::value clone = json;
assert(json == clone);
// extract into user friendly datastructure from the question:
auto extracted = Data::extract_from(json);
for (auto& e : extracted.folders) std::cout << "folder:\t" << e.id << "\t" << e.path << "\n";
for (auto& e : extracted.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.png
file: 25 /1/105/110/ another_picture.jpg
答案 1 :(得分：2)
因为另一个答案was deemed "very complex"中的数据结构和目标数据结构是suggested to be：
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;
};
我最终写了一个来自泛型＆＃34; JSON＆＃34;到该数据结构（参见其他答案： Reading JSON file with C++ and BOOST ）。
但是，如果我们跳过中间人，那么OP也许会更高兴。并将JSON专门解析为显示的Data结构。这＆＃34;简化了＆＃34;语法使其仅适用于此类文档：
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
优点：
最后一个好处有另一面：如果你想要阅读稍微不同的JSON，现在你需要使用语法，而不是仅仅编写不同的提取/转换。在37行代码中，我的偏好是other answer，但我会留给您决定。
这是直接使用此语法的相同演示程序：
<强> Live On Coliru
//#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 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>
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.png
file: 25 /1/105/110/ another_picture.jpg
答案 2 :(得分：-1)