[Solved] Parsing a JSon reply issue

andre

Sounds like you are not using C++/11, which is needed for this code to work.

roseicollis

Yes, that was the first error i solved. I put it on the .pro file as

QMAKE_CXXFLAGS += -std=c++11
and tried too with
QMAKE_CXXFLAGS += -std=gnu++11

And the compile output gaves something like:

@
g++ -c -pipe -std=c++11 -g -Wall -W -D_REENTRANT -DQT_SCRIPT_LIB -DQT_GUI_LIB -DQT_NETWORK_LIB -DQT_CORE_LIB -DQT_SHARED -I/usr/lib/qt4/mkspecs/linux-g++[...]@

andre

Did you try with simply putting
@
CONFIG += c++11
@
in your .pro file?

roseicollis

Then I get the same error I had first:

/usr/lib/gcc/i686-redhat-linux/4.7.2/../../../../include/c++/4.7.2/bits/c++0x_warning.h:32:2: error: #error This file requires compiler and library support for the ISO C++ 2011 standard. This support is currently experimental, and must be enabled with the -std=c++11 or -std=gnu++11 compiler options.

Which I solved with
@
QMAKE_CXXFLAGS = -std=c++11

(and even with the next line instead of the other the error dissapears)
QMAKE_CXXFLAGS = -std=gnu+11
@

The error I was saying is in line 197:
@
for (auto& element : a)
{
value_.object->emplace(std::make_pair(std::move(element[0]), std::move(element[1]))); // HERE IS THE ERROR
}
@

roseicollis

I've found this other solution: "JSon":https://github.com/gaudecker/qt-json

It seems that it works but now I can't get the name and code values, I'm trying to do:

@
bool ok;

QtJson::JsonObject result = QtJson::parse(myJson, ok).toMap();
if(!ok) {
qFatal("An error occurred during parsing");
}else
{
qDebug() << "data" << result["data"].toString();
qDebug() << " try1" << result["Name"].toString();

QtJson::JsonObject nested = result["data"].toMap();
qDebug() << "try2:" << nested["Name"].toString();

@

But try1 and try2 are empy. Any Idea of how to make that work?

Thanks!

JKSH

Hi,

[quote author="roseicollis" date="1423496917"]But try1 and try2 are empy. Any Idea of how to make that work?[/quote]Your data is a JSON array, not a JSON object.

roseicollis

Oh I see...

But if I put:
@
QtJson::JsonArray nested = result["data"].toMap();
qDebug() << "try2:" << nested["Name"].toString();
@

It says:
@
conversion from 'QMap<QString, QVariant>' to non-scalar type 'QtJson::JsonArray {aka QList<QVariant>}' requested
@

I don't really know how to parse that array... I've tried this too:

@
QtJson::JsonObject bbb = QtJson::parse(result["data"].toString(), ok).toMap();
qDebug() << bbb;
@
But it only prints: QMap()

So... I'm really stuck there... -.-''

JKSH

Are you familiar with JSON syntax?

represents an array.
{ } represents an object.

You need to understand your structure first: You have 1 array. That array contains 2 objects. Each object contains 2 strings

Extract the objects from the array like this:
@
auto object1 = result[0];
auto object2 = result[1];
@

After that, you can extract the "Name" and "data" fields from the objects.

Remember, arrays are indexed by integers, while objects/maps are indexed by strings.

roseicollis

Hi JKSH,

Ermmm noup, I wasn't familiar with it but now I understand it better :) Thanks!

One thing: what is auto for you? O.o a JsonObject?

@
QtJson::JsonObject object1 = result[0].toMap(); //object1 returns: QMap()
QVariant object1 = result[0]; //object1 returns: QVariant(, )
QVariant object1 = result[0].toString();//object1 returns: QVariant(QString, )
@

EDIT: Didn't know there were something called 'auto' O.o but trying that:

@
QtJson::JsonObject result = QtJson::parse(myJson, ok).toMap();
auto object1 = result[0];
QtJson::JsonObject trying = QtJson::parse(object1, ok).toMap();
qDebug() <<" trying msg" << trying;
@

it says: error: no matching function for call to 'parse(QVariant&, bool&)'
And if I try with
@
QtJson::JsonObject trying = QtJson::parse(object1["Name"], ok).toMap();
@
It says: error: no match for 'operator[]' in 'object1["Name"]'

JKSH

You're welcome. :)

[quote author="roseicollis" date="1423567075"]
@
QtJson::JsonObject result = QtJson::parse(myJson, ok).toMap();
@
[/quote]2 issues:

Like I said before, your data is an array, not an object. So, you should make result a JsonArray, not a JsonObject. Also, toMap() produces an object. You want to use toList() instead, which produces an array.

What type is myJson? Your compiler complained because you passed a QVariant into QtJson::parse(). What type does it actually accept? (hint: look inside json.h)

[quote author="roseicollis" date="1423567075"]EDIT: Didn't know there were something called 'auto' O.o[/quote]'auto' is a "C++11 keyword":http://geekswithblogs.net/BlackRabbitCoder/archive/2012/03/15/c-little-wonders-the-c11-auto-keyword-redux.aspx. When you use it, the compiler will try to figure out the variable's type automatically.

roseicollis

Hi again ^^

[quote author="JKSH" date="1423568300"]
Like I said before, your data is an array, not an object. So, you should make result a JsonArray, not a JsonObject. Also, toMap() produces an object. You want to use toList() instead, which produces an array.
[/quote]
Didn't know that it creates an object too... (anyway i tried before with strings and bytearray hopeing something works hahaha but not obviously)

[quote author="JKSH" date="1423568300"]
What type is myJson? Your compiler complained because you passed a QVariant into QtJson::parse(). What type does it actually accept? (hint: look inside json.h)
[/quote]

myJson is a QString:
@
QNetworkRequest request(_Url);
QNetworkReply *reply = nam->get(request);
QString myJson = (QString)reply->readAll();
@

I know that this error is because of the types but I was thinking that it takes Variants and now saw that not. The definition of parse is:
@
QVariant parse(const QString &json, bool &success);
@

If I try with:
@
QtJson::JsonArray result = QtJson::parse(myJson, ok).toList();
qDebug() << " a " << result;
auto object1 = result[0];
qDebug() << " a1 " << object1;
@

Then it prints:
a()
ASSERT failure in QList<T>::operator[]: "index out of range",

Which is normal if a() is empty O.o

I'll have to inquire about what c++11 is, really thank you so much! Now I have new weekend reading :D

JKSH

Hmm... what do you get if you do this?

@
qDebug() << myJson;
qDebug() << QtJson::parse(myJson, ok);
qDebug() << ok;
@

C++11 is the updated version of C++ which came out in 2011 :) It offers lots of new language features to make C++ more powerful and easier to use. C++14 is in the works, but it's no longer 2014 now so the update will probably be called C++15 instead.

roseicollis

This returns the next:

@
"{"data":"[{"Name":"One","Code":""},{"Name":"Two","Code":"Alpha"}]"}"

QVariant(QVariantMap, QMap(("data", QVariant(QString, "[{"Name":"One","Code":""},{"Name":"Two","Code":"Alpha"}]") ) ) )

true
@

wooow I thought there were only C, C# and C++ .... what an inonce girl I am XDDDD I will definitely look more about it at the weekend, it sounds really interesting!

JKSH

[quote author="roseicollis" date="1423572240"]
@
"{"data":"[{"Name":"One","Code":""},{"Name":"Two","Code":"Alpha"}]"}"
@

[/quote]I'm so sorry... I though myJson was
@
[{"Name":"One","Code":""},{"Name":"Two","Code":"Alpha"}]
@

...that's why I thought your data was an array of 2 objects. :( Sorry for sending you on a wild goose chase!

Anyway, your actual JSON data is: 1 object which contains 1 string value. I must say your data is formatted quite strangely (where did you get it from?).

So, in the first run, you can only extract one string:
@
QtJson::JsonObject outerObject = QtJson::parse(myJson, ok).toMap();
QString innerString = outerObject.toString();

qDebug() << myJson;
qDebug() << innerString;
@

You will see that myJson contains lots of '' characters, but innerString doesn't. That's because the data in outerObject is escaped -- the JSON parser treats it as a single string instead of a JSON array.

Anyway, after parsing it the first time, you now have un-escaped data in innerString, so you can send it through the JSON parser again to extract the array:

@
QtJson::JsonArray outerArray = QtJson::parse(innerString, ok).toList();

qDebug() << ok;
qDebug() << outerArray;
@

Now, you can apply my previous posts.

Good luck!

[quote author="roseicollis" date="1423572240"]wooow I thought there were only C, C# and C++ .... what an inonce girl I am XDDDD I will definitely look more about it at the weekend, it sounds really interesting![/quote]There are lots and lots of programming languages out there. :) C, C# and C++ are different languages.

However, C++03, C++11, and C++14 are different versions of the same language.

Happy reading!

roseicollis

[quote author="JKSH" date="1423574139"]
. :( Sorry for sending you on a wild goose chase!
[/quote]
No problem! I learnt a lot with that too :D

[quote author="JKSH" date="1423574139"]
I must say your data is formatted quite strangely (where did you get it from?)
[/quote]

I don't know which should be its structure but this is what I will receive from a webservice which is made by a work mate and the only thing I know is: I have to parse it and show it on a widget (Still dunno if combobox or what will be the best option)

[quote author="JKSH" date="1423574139"]
@
QtJson::JsonObject outerObject = QtJson::parse(myJson, ok).toMap();
QString innerString = outerObject.toString();

qDebug() << myJson;
qDebug() << innerString;
@
[/quote]

I had to make some changes to make it work:

@
QtJson::JsonObject outerObject = QtJson::parse(myJson, ok).toMap();
QString innerString = outerObject["data"].toString();
qDebug() << myJson;
qDebug() << innerString;
QtJson::JsonArray outerArray = QtJson::parse(innerString, ok).toList();
qDebug() << ok;
qDebug() << outerArray;
auto object1 = outerArray[0].toMap();
qDebug() << " DD" << object1["Name"];
@

So:

DD returns: DD QVariant(QString, "One")

Now I'm trying to get that "One" string alone but at least I can see it!! I'm almost there, so cloose!

[quote author="JKSH" date="1423574139"]
There are lots and lots of programming languages out there. :) C, C# and C++ are different languages.
However, C++03, C++11, and C++14 are different versions of the same language.
[/quote]

Yes, I know there are soo many programming languages but didn't think about versions.. Never though they exist for the languages too haha

JKSH

[quote author="roseicollis" date="1423581028"]I had to make some changes to make it work:[/quote]Good catch!

[quote author="roseicollis" date="1423581028"]So:

DD returns: DD QVariant(QString, "One")

Now I'm trying to get that "One" string alone but at least I can see it!! I'm almost there, so cloose![/quote]Yep, almost there! :) object1["Name"] is a QVariant, so see http://doc.qt.io/qt-5/qvariant.html for clues

[quote author="JKSH" date="1423574139"]Yes, I know there are soo many programming languages but didn't think about versions.. Never though they exist for the languages too haha[/quote]I think Shakespeare's English and modern English are 2 different versions of English ;-P

roseicollis

[quote author="JKSH" date="1423582568"]
Yep, almost there! :) object1[“Name”] is a QVariant, so see http://doc.qt.io/qt-5/qvariant.html for clues
[/quote]
Yesterday I was trying with object1["Name"].toString() but it was saying all time that there were no func like toString()... today I tried it again because it sounds logical for me and now it works... -. -'' I really hate programing when that happens hahahaha... anyway, it works :D So I'm happy :D

[quote author="JKSH" date="1423582568"]
I think Shakespeare’s English and modern English are 2 different versions of English ;-P
[/quote]
Wooow, do you really think that?? O.o I thought that the english nowadays was the same as shakespears or as the cavemen.. :P I was just joking ^.^ Haha that is a really really nice example!

Thank you for all your help guys! And special thanks for you JKSH. I have enjoyed so much this problem and learnt a lot! :D

JKSH

You're most welcome :)

Happy coding!