为什么 Boost 属性树 write_json 将所有内容保存为字符串？有可能改变吗？

Why does Boost property tree write_json save everything as string? Is it possible to change that?

提问by pprzemek

I'm trying to serialize using boost property tree write_json, it saves everything as strings, it's not that data are wrong, but I need to cast them explicitly every time and I want to use them somewhere else. (like in python or other C++ json (non boost) library)

我正在尝试使用 boost 属性树 write_json 进行序列化，它将所有内容保存为字符串，并不是数据错误，但我每次都需要显式转换它们，并且我想在其他地方使用它们。（如在 python 或其他 C++ json（非 boost）库中）

here is some sample code and what I get depending on locale:

这是一些示例代码以及我根据语言环境得到的内容：

boost::property_tree::ptree root, arr, elem1, elem2;
elem1.put<int>("key0", 0);
elem1.put<bool>("key1", true);
elem2.put<float>("key2", 2.2f);
elem2.put<double>("key3", 3.3);
arr.push_back( std::make_pair("", elem1) );
arr.push_back( std::make_pair("", elem2) );
root.put_child("path1.path2", arr);

std::stringstream ss;
write_json(ss, root);
std::string my_string_to_send_somewhare_else = ss.str();

and my_string_to_send_somewhere_elseis sth. like this:

并且my_string_to_send_somewhere_else是…… 像这样：

{
    "path1" :
    {
       "path2" :
       [
            {
                 "key0" : "0",
                 "key1" : "true"
            },
            {
                 "key2" : "2.2",
                 "key3" : "3.3"
            }
       ]
    }
}

Is there anyway to save them as the values, like: "key1" : trueor "key2" : 2.2?

无论如何将它们保存为值，例如： "key1" : true或"key2" : 2.2？

采纳答案by sbile

The simplest and cleanest solution that i could come up with was generating the JSON with placeholders and in the end string replacing with the actual value ditching the extra quotes.

我能想到的最简单、最干净的解决方案是生成带有占位符的 JSON，最后用实际值替换掉额外的引号。

static string buildGetOrdersCommand() {
    ptree root;
    ptree element;
    element.put<string>("pendingOnly", ":pendingOnly");
    element.put<string>("someIntValue", ":someIntValue");

    root.put("command", "getOrders");
    root.put_child("arguments", element);

    std::ostringstream buf;
    write_json(buf, root, false);
    buf << std::endl;

    string json = buf.str();
    replace(json, ":pendingOnly", "true");
    replace(json, ":someIntValue", std::to_string(15));

    return json;
}

static void replace(string& json, const string& placeholder, const string& value) {
    boost::replace_all<string>(json, "\"" + placeholder + "\"", value);
}

And the result is

结果是

{"command":"getOrders","arguments":{"pendingOnly":true,"someIntValue":15}}

{"command":"getOrders","arguments":{"pendingOnly":true,"someIntValue":15}}

回答by pprzemek

Ok, I've solved it like this, (of course it won't suite for everybody, as it is a bit of a hack, that need further work).

好的，我已经这样解决了，（当然它不会适合所有人，因为它有点黑客，需要进一步的工作）。

---

---

I've wrote my own write_jsonfunction (simply copied the files, json_parser.hppand json_parser_write.hppto my project) and modified the following lines in json_parser_write.hpp:

[我已写我自己的write_json功能（简单复制的文件，json_parser.hpp并json_parser_write.hpp到我的项目），并修改了以下几行json_parser_write.hpp：

1. commented line 37 - escaping the quote '"'
2. changed line 76 - so that it doesn't add quotes anymore: stream << Ch('"') << data << Ch('"'); ==> stream << data;

1. 注释第 37 行 - 转义引号 '"'
2. 更改了第 76 行 - 使其不再添加引号： stream << Ch('"') << data << Ch('"'); ==> stream << data;

---

---

Then values will be saved properly except for strings, so I wrote custom translator for it:

然后值将被正确保存，除了字符串，所以我为它编写了自定义翻译器：

template <typename T>
struct my_id_translator
{
    typedef T internal_type;
    typedef T external_type;

    boost::optional<T> get_value(const T &v) { return  v.substr(1, v.size() - 2) ; }
    boost::optional<T> put_value(const T &v) { return '"' + v +'"'; }
};

and simply saved string using:

并简单地使用以下方法保存字符串：

elem2.put<std::string>("key2", "asdf", my_id_translator<std::string>());

complete program:

完整程序：

#include <iostream>
#include <string>
#include <sstream>

#include <boost/property_tree/ptree.hpp>

#include "property_tree/json_parser.hpp" // copied the headers

template <typename T>

struct my_id_translator
{
    typedef T internal_type;
    typedef T external_type;

    boost::optional<T> get_value(const T &v) { return  v.substr(1, v.size() - 2) ; }
    boost::optional<T> put_value(const T &v) { return '"' + v +'"'; }
};

int main(int, char *[])
{
    using namespace std;
    using boost::property_tree::ptree;
    using boost::property_tree::basic_ptree;
    try
    {
        ptree root, arr,elem2;
        basic_ptree<std::string, std::string> elem1;
        elem1.put<int>("int", 10 );
        elem1.put<bool>("bool", true);
        elem2.put<double>("double", 2.2);
        elem2.put<std::string>("string", "some string", my_id_translator<std::string>());

        arr.push_back( std::make_pair("", elem1) );
        arr.push_back( std::make_pair("", elem2) );
        root.put_child("path1.path2", arr);

        std::stringstream ss;
        write_json(ss, root);
        std::string my_string_to_send_somewhere_else = ss.str();

        cout << my_string_to_send_somewhere_else << endl;

    }
    catch (std::exception & e)
    {
        cout << e.what();
    }
    return 0;
}

result :)

结果 ：）

{
    "path1":
    {
        "path2":
        [
            {
                "int": 10,
                "bool": true
            },
            {
                "double": 2.2,
                "string": "some string"
            }
        ]
    }
}

回答by Alex Sed

Boost confirms its implementation has no 100% conformance to JSON standard. Check the following link to see their explanation: Making a ptree variant that preserves JSON types is a future plan, but far off.!

Boost 确认其实现没有 100% 符合 JSON 标准。检查以下链接以查看他们的解释： 制作保留 JSON 类型的 ptree 变体是未来的计划，但还很遥远。！

回答by Josbert Lonnee

As we have typedef basic_ptree<std::string, std::string> ptree; in the boost libraries, boost will always serialize each value as string and parse all values to a string equivalent.

因为我们有 typedef basic_ptree<std::string, std::string> ptree; 在 boost 库中，boost 总是将每个值序列化为字符串，并将所有值解析为等效的字符串。

回答by Sean Kinsey

From the outputted JSON it is clear that the serializer serializes everything to strings using some sort of .toString() method - that is, its unaware of the type of each member and so encloses everything in " ".

从输出的 JSON 中可以清楚地看出，序列化程序使用某种 .toString() 方法将所有内容序列化为字符串——也就是说，它不知道每个成员的类型，因此将所有内容都包含在“”中。

See Creating JSON arrays in Boost using Property Treesfor more about this problem .

有关此问题的更多信息，请参阅使用属性树在 Boost 中创建 JSON 数组。

回答by Sean Kinsey

I ended up adding another function to my utils to solve this:

我最终向我的实用程序添加了另一个函数来解决这个问题：

#include <string>
#include <regex>
#include <boost/property_tree/json_parser.hpp>

namespace bpt = boost::property_tree;
typedef bpt::ptree JSON;
namespace boost { namespace property_tree {
    inline void write_jsonEx(const std::string & path, const JSON & ptree)
    {
        std::ostringstream oss;
        bpt::write_json(oss, ptree);
        std::regex reg("\\"([0-9]+\.{0,1}[0-9]*)\\"");
        std::string result = std::regex_replace(oss.str(), reg, "");

        std::ofstream file;
        file.open(path);
        file << result;
        file.close();
    }
} }

Hope that helps.

希望有帮助。