Rapidjson: Parse an array of objects in C++ using rapidjson.

[srikarad07]

I'm trying to parse the following JSON file in c++. I would like to iterate over the 'attributes' array and obtain the value of the string:'value' for a specific value of a string:'name' of that attribute object. For ex: I would like to parse this JSON file and obtain the 'value' for 'mass'.

~js
{
"active": true,
"apiTier": 0,
"attributes": [
{
"description": "Given in the datasheet as '0.33 kg (0.73 lbm)'.",
"maximumValue": "",
"measurementUnit": "kg",
"minimumValue": "",
"name": "mass",
"productConfiguration": "base",
"value": "0.33"
},
{
"description": "",
"maximumValue": "",
"measurementUnit": "",
"minimumValue": "",
"name": "propellant-type",
"productConfiguration": "base",
"value": "hydrazine"
},
{
"description": "Given in the datasheet as 'Thrust/Steady State' and the specified value is also reported as '(0.05-0.230) lbf'.",
"maximumValue": "1.02",
"measurementUnit": "N",
"minimumValue": "0.22",
"name": "thrust",
"productConfiguration": "base",
"value": ""
}
]
~

I am trying to do this in C++ using rapidjson library to parse the JSON file. Below is my implementation for the parsing of the JSON file. What I would like to do is within the for loop, for a specific 'value' for a string 'name' (for ex: mass) obtain the other 'values' for string such as 'maximumValue', 'minimumValue', 'value' etc.

~~~cpp

include

include

include

include

int main()
{
std::ifstream inputFile( "/path/to/json/file/" );
std::stringstream jsonDocumentBuffer;
std::string inputLine;

while ( std::getline( inputFile, inputLine ) )
{
jsonDocumentBuffer << inputLine << "\n";
}
rapidjson::Document config;
config.Parse( jsonDocumentBuffer.str( ).c_str( ) );

rapidjson::Value::MemberIterator attributeIterator = config.FindMember( "attributes" );
int counter = 0;
const rapidjson::Value& attributes = config[ "attributes" ];
for ( rapidjson::Value::ConstMemberIterator iterator = attributes.MemberBegin(); iterator != attributes.MemberEnd(); ++iterator )
{
std::cout << ++counter << std::endl;
}
}
~~~

[miloyip]

Since attributes is an array (you may check it with attributes.IsArray(), so you should iterates the array first:

~cpp
assert(attributes.IsArray()); // attributes is an array
for (rapidjson::Value::ConstValueIterator itr = attributes.Begin(); itr != attributes.End(); ++itr) {
const rapidjson::Value& attribute = *itr;
assert(attribute.IsObject()); // each attribute is an object
for (rapidjson::Value::ConstMemberIterator itr2 = attribute.MemberBegin(); itr2 != attribute.MemberEnd(); ++itr2) {
std::cout << itr2->name.GetString() << " : " << itr2->value.GetString() << std::endl;
}
}
~

[srikarad07]

Thanks for your answer!

My question was to obtain the value of string such as ('value', 'maximumValue', etc..) for a specific value (Eg: mass) for the string 'name'. However, the above code iterates over all the strings and extract their specific values.

A small edit: In the above code I get an error for using 'rapidjson::Value:: ConstIterator'. I looked around on the rapidjson tutorials and noticed it is 'rapidjson::Value::ConstValueIterator'.

[miloyip]

So you need to firstly find which attribute is "mass", and then obtain the properties.
I fixed the above example.

[srikarad07]

Yup, exactly that's what I need to do.

[wangsongyuan98]

I don't think the above example is fixed as I cannot see where did you obtain the "mass" property. Can you please add it again. Thank you!