Parsing JSON with duplicate keys (json-cpp)

Question

I'm using JsonCpp v0.6.0 to parse the following JSON string:

{
   "3.7":"de305d54-75b4-431b-adb2-eb6b9e546011",
   "3.7":"de305d54-75b4-431b-adb2-eb6b9e546012",
   "3.8":"de305d54-75b4-431b-adb2-eb6b9e546013"
}

as follows:

    Json::Value  root;
    Json::Reader reader;

    // value contains the JSON string

    if (!reader.parse(value, root, false))
    {
        // parse error
    }

After the call to parse, root contains two entries in a map:

[0] first = "3.7", second = "de305d54-75b4-431b-adb2-eb6b9e546012",
[1] first = "3.8", second = "de305d54-75b4-431b-adb2-eb6b9e546013",

i.e. the first JSON record has been overwritten by the second. No errors are reported.

Is this behaviour expected? Is it correct?

I thought that an error might have been reported indicating that there is a duplicate key in the JSON string.

Answer 1

Like the JSON RFC sad the object names (keys) should be unique.

The names within an object SHOULD be unique.

Also the RFC defines if they are not, the behavior is unpredictable.

See this quote from the RFC:

An object whose names are all unique is interoperable in the sense
that all software implementations receiving that object will agree on the name-value mappings. When the names within an object are not
unique, the behavior of software that receives such an object is
unpredictable. Many implementations report the last name/value pair
only. Other implementations report an error or fail to parse the
object, and some implementations report all of the name/value pairs,
including duplicates.