c++ - 使用 boost property_tree 创建 json 数组

Question

我在使用 C++ 中的 boost 库和属性树创建 json 数组时遇到了麻烦。

我引用了this线程，尤其是这部分

ptree pt;
ptree children;
ptree child1, child2, child3;


child1.put("childkeyA", 1);
child1.put("childkeyB", 2);

child2.put("childkeyA", 3);
child2.put("childkeyB", 4);

child3.put("childkeyA", 5);
child3.put("childkeyB", 6);

children.push_back(std::make_pair("", child1));
children.push_back(std::make_pair("", child2));
children.push_back(std::make_pair("", child3));

pt.put("testkey", "testvalue");
pt.add_child("MyArray", children);

write_json("test2.json", pt);

结果:

{
    "testkey": "testvalue",
    "MyArray":
    [
        {
            "childkeyA": "1",
            "childkeyB": "2"
        },
        {
            "childkeyA": "3",
            "childkeyB": "4"
        },
        {
            "childkeyA": "5",
            "childkeyB": "6"
        }
    ]
}

但是如果我只想实现一个没有任何对象包含它的简单数组，我该怎么办呢？像这样:

[
    {
        "childkeyA": "1",
        "childkeyB": "2"
    },
    {
        "childkeyA": "3",
        "childkeyB": "4"
    },
    {
        "childkeyA": "5",
        "childkeyB": "6"
    }
]

非常感谢。

Answer 1

关于 JSON 支持的 Boost 文档只有几行:

http://www.boost.org/doc/libs/1_63_0/doc/html/property_tree/parsers.html#property_tree.parsers.json_parser

The property tree dataset is not typed, and does not support arrays as such. Thus, the following JSON / property tree mapping is used:

• JSON objects are mapped to nodes. Each property is a child node.
• JSON arrays are mapped to nodes. Each element is a child node with an empty name. If a node has both named and unnamed child nodes, it cannot be mapped to a JSON representation.
• JSON values are mapped to nodes containing the value. However, all type information is lost; numbers, as well as the literals "null", "true" and "false" are simply mapped to their string form.
• Property tree nodes containing both child nodes and data cannot be mapped.

JSON round-trips, except for the type information loss.

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