simpler way to access a Json variable
Added by Bruno Zerbo almost 6 years ago
I have a Json string that I have successfully parsed to get the variable value in this manner:
std::string stringwithJson = "....Json code..."
Json::Object result;
Json::parse(stringwithJson, result);
//I'm trying to get the variable inside result::routes[0]::legs[0]::steps[2]::distance::value
Json::Array routes = result["routes"];
Json::Array legs = static_cast<Json::Object>(routes.at(0)).get("legs");
Json::Array steps = static_cast<Json::Object>(legs.at(0)).get("steps");
Json::Object steps_2= steps.at(2);
Json::Object distance = steps_2["distance"];
int value = distance["value"];
std::cout << "Distance value = " << value << std::endl;
I'm writing 6 lines of code to get my variable. Is there a simpler way?
It would be beautiful to may write somethings like result.get("routes").at(0).get("legs").at(0).get("steps").at(2).get("distance").value but we can't due to the necessity di cast.
Maybe It is the cost to pay to use c in place of , for example, .NET.
Thanks for reply
Replies (4)
RE: simpler way to access a Json variable - Added by Bruno Zerbo almost 6 years ago
My Json code is
{
"geocoded_waypoints" : [
{
"geocoder_status" : "OK",
"place_id" : "ChIJzeQPphVYERMRYEK4ZykECwQ",
"types" : [ "administrative_area_level_3", "political" ]
},
{
"geocoder_status" : "OK",
"place_id" : "ChIJ4UgtC5r7ExMRPI9qYCPgIj8",
"types" : [ "locality", "political" ]
}
],
"routes" : [
{
"bounds" : {
"northeast" : {
"lat" : 37.555756,
"lng" : 15.1449201
},
"southwest" : {
"lat" : 37.5205644,
"lng" : 15.020874
}
},
"copyrights" : "Map data ©2019",
"legs" : [
{
"distance" : {
"text" : "15.1 km",
"value" : 15102
},
"duration" : {
"text" : "27 mins",
"value" : 1645
},
"end_address" : "95021 Aci Castello, Province of Catania, Italy",
"end_location" : {
"lat" : 37.555756,
"lng" : 15.1444998
},
"start_address" : "95045 Misterbianco, Province of Catania, Italy",
"start_location" : {
"lat" : 37.5292177,
"lng" : 15.020874
},
"steps" : [
{
"distance" : {
"text" : "0.3 km",
"value" : 307
},
"duration" : {
"text" : "1 min",
"value" : 55
},
"end_location" : {
"lat" : 37.5278512,
"lng" : 15.0226143
},
"html_instructions" : "Head \u003cb\u003esoutheast\u003c/b\u003e on \u003cb\u003eVia della Campana\u003c/b\u003e toward \u003cb\u003eVia Mario Moschetti\u003c/b\u003e",
"polyline" : {
"points" : "s|`dFmwtzAHIJKRQPKn`_@FCFCDCJItA_BLOf@k@f@i@LQNU@C@A?C?AAC?CACAAAACACAC?E?C@QFa`P"
},
"start_location" : {
"lat" : 37.5292177,
"lng" : 15.020874
},
"travel_mode" : "DRIVING"
},
{
"distance" : {
"text" : "84 m",
"value" : 84
},
"duration" : {
"text" : "1 min",
"value" : 14
},
"end_location" : {
"lat" : 37.5273584,
"lng" : 15.0233117
},
"html_instructions" : "Sharp \u003cb\u003eright\u003c/b\u003e to stay on \u003cb\u003eVia della Campana\u003c/b\u003e",
"maneuver" : "turn-sharp-right",
"polyline" : {
"points" : "at`dFibuzA?G`C@C@E@C@AFIPSb@g@`CJKBGFQ"
},
"start_location" : {
"lat" : 37.5278512,
"lng" : 15.0226143
},
"travel_mode" : "DRIVING"
},
{
"distance" : {
"text" : "1.8 km",
"value" : 1785
},
"duration" : {
"text" : "4 mins",
"value" : 238
},
"end_location" : {
"lat" : 37.5368933,
"lng" : 15.0385343
},
etc etc
RE: simpler way to access a Json variable - Added by Roel Standaert almost 6 years ago
Why .NET as an example? C# is also a statically typed language.
Other JSON libraries do it differently, e.g. probably the most well-known one infers that you want to use it as an array if you use operator[] with an integer key, or as an object if you use operator[] with a string key.
Wt's JSON implementation is a very minimal implementation. Maybe we could consider supplanting it with another implementation rather than iterating on it. I don't consider Wt's JSON implementation a key feature of Wt.
In any case, you can always use another implementation if Wt's implementation is not to your liking.
RE: simpler way to access a Json variable - Added by Roel Standaert almost 6 years ago
Note: you're doing a lot of copies. You should be able to do a static_cast<Json::Object&> rather than static_cast<Json::Object>, and static_cast<Json::Array&> rather than static_cast<Json::Array>.
RE: simpler way to access a Json variable - Added by Bruno Zerbo almost 6 years ago
Thank you. I forgot to use a reference instead of the copy.