Boost read_json is not working with wptree from std::wstring

Question

I have a simple code which is not working and I don't really know why... here it's:

std::wstring CDbFilterSerializer::DeserializeFromString(const std::wstring& jsonStr)
{
    std::wistringstream ss{ jsonStr };
    boost::property_tree::read_json(ss, m_root);
    return m_root.data();
}

The problem here is that after calling m_root.read_json(...) the wptre object is empty. The return statement is an example, cause the real code after populating the wptree object, I call m_root.get("MyKey") to start reading values and this throw an exception cause the object is empty.

The json received as parameter is:

{
"type":{
      "className":"NumericFilterSerializerHelper: NumericType => unsigned int, DbSerializer => class CDbFilterSerializerByNumericValue",
      "description":""
   },
   "data":{
      "int_number":"45"
   }
}

Is there something wrong here?

@JasonAller let's keep all the boost- tags prefixed consistently. `ptree` is not a thing in software - and if it is, it has nothing to do with `boost-propertytree`. I realize `ptree` exists, but it should be merged with the more frequent [tag:boost-propertytree] — sehe, Dec 15 '21 at 18:31
@sehe did you mean to tag me in that comment, or the author who used the tag? — Jason Aller, Dec 15 '21 at 18:40
@JasonAller Ah, I couldn't see the edit so I surmised it must have been the tags. That's not the case, so sorry to bother you :) — sehe, Dec 15 '21 at 22:18

score 1 · Accepted Answer · answered Dec 15 '21 at 11:37

Yes. The assumptions are wrong. .data() returns the value at the root node, which is empty (since it's an object). You can print the entire m_tree to see:

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

struct CDbFilterSerializer {
    std::wstring DeserializeFromString(const std::wstring& jsonStr);

    boost::property_tree::wptree m_root;
};

std::wstring CDbFilterSerializer::DeserializeFromString(const std::wstring& jsonStr)
{
    std::wistringstream ss{ jsonStr };
    read_json(ss, m_root);
    return m_root.data();
}

int main() {
    CDbFilterSerializer obj;
    obj.DeserializeFromString(LR"({
"type":{
      "className":"NumericFilterSerializerHelper: NumericType => unsigned int, DbSerializer => class CDbFilterSerializerByNumericValue",
      "description":""
   },
   "data":{
      "int_number":"45"
   }
})");

    write_json(std::wcout, obj.m_root, true);
}

Which prints

{
    "type": {
        "className": "NumericFilterSerializerHelper: NumericType => unsigned int, DbSerializer => class CDbFilterSerializerByNumericVa
lue",
        "description": ""
    },
    "data": {
        "int_number": "45"
    }
}

As you can see the object is not empty. You probably have the path misspelled (we can't tell because MyKey is not in your document).

SIDE NOTE

Do not abuse Property Tree for JSON "support". Instead use a JSON library! Boost JSON exists. Several others are freely available.

Boost read_json is not working with wptree from std::wstring

1 Answers1

SIDE NOTE