Use this tag for questions related to nlohmann JSON C++ library
nlohmann JSON is a header-only JSON class for Modern C++ (C++11)
Latest release: 3.9.1 released on 2020-08-06
See the github project
Questions tagged [nlohmann-json]
248 questions
3
votes
2 answers
Nlohmann::json& as function argument without including json.hpp in header
I have a class where I want to have a function that uses nlohmann::json& as the argument:
class MyClass
{
public:
void foo(nlohmann::json& node);
};
But I don't want to include the json.hpp file in my header, just my .cpp. How can I declare…
Chip Burwell
- 423
- 3
- 10
3
votes
2 answers
Json data creation for nlohmann
I have some data like
{
"GLOBAL DATA":
{
"FIRST": [
{"BEGIN": "0", "END" : "100"}
],
"SECOND":"SomeData",
"THIRD":"SomeMoreData"
}
}
I want to add more data to FIRST array.
I tried creating the…
Sreeraj Chundayil
- 5,548
- 3
- 29
- 68
3
votes
2 answers
Array or object: how to use nlohmann::json for simple use cases?
I want to use the nlohmann JSON library in order to read options from a JSON file. Specifying options is optional, as reflected in the constructor in my code example. I'm assuming the JSON structure is an object in its root.
Unfortunately, I'm…
Wouter Beek
- 3,307
- 16
- 29
3
votes
1 answer
Calling method nlohmann::json::dump from visual studio intermediate window
I'm trying to dump object from type nlohmann::json into readable string value from visual studio debugger. So in order to invoke the dump method from the nlohmann::json instance, i use visual studio intermediate window.
However, it seems like this…
Irad K
- 867
- 6
- 20
3
votes
1 answer
nlohmann's json library convert an array to a vector of structs
Say I have a json array that looks like this:
[
{
"Name": "test",
"Val": "test_val"
},
{
"Name": "test2",
"Val": "test_val2"
}
]
I want to convert this into a vector of structs:
struct Test {
string Name;
string…
Ank i zle
- 2,089
- 3
- 14
- 36
3
votes
1 answer
How can I get the array length in nlohmann's json library?
I am using nlohmann/json lib and want to get the length of a json array. Image i have:
[
"test",
"test2"
]
and want to recieve the length (2). When i tried the .length() method, it showed me this error:
using json = using json = class…
Ank i zle
- 2,089
- 3
- 14
- 36
3
votes
0 answers
Unknown breakpoint in nlohmann/json framework
Since some time, when I run my app under Xcode with breakpoints enabled, I hit a unknown breakpoint apparently in a system framework called nlohmann::basic_json:
I can continue execution without problems, but this is annoying anyway.
Any idea…
Reinhard Männer
- 14,022
- 5
- 54
- 116
3
votes
1 answer
nlohmann JSON, change the value of a key
I'm using nlohmann::json and all I need to do is copy a JSON object and then alter some of the keys in it. Is it possible to alter keys in nlohmann::json objects?
Essentially what I'm trying to do is the following:
json obj1 = {"key with space" :…
Nick Chapman
- 4,402
- 1
- 27
- 41
2
votes
1 answer
Strange behaviour when using nlohmann-json
I have the following function:
// get-function that can handle nullptr.
template
static const T get(const nlohmann::json& json, const T& retOnNull = T())
{
return json.is_null() ? retOnNull : json.get();
}
Then I call it like…
DaedalusAlpha
- 1,610
- 4
- 20
- 33
2
votes
1 answer
Unexpected implicit conversion from nlohmann::json to string
While debugging an application I came up with the following example:
#include
using nlohmann::json;
struct X {
X(const std::string& s){}
};
int main() {
X x("{}"_json); // why compiler allows this?
}
See at…
Dmitriy Kumshayev
- 228
- 3
- 12
2
votes
0 answers
Copy json, but update only keys that exists in target
I have two JSON objects, original and current.
The original object was created by reading a configuration file, it have a certain specific keys.
The current object was created as a copy of original, then there are keys added to current, as well as…
Some programmer dude
- 400,186
- 35
- 402
- 621
2
votes
1 answer
How to convert json to cpp class using nlohmann::json macros?
I am trying to map json data to a class called Game by using the macro NLOHMANN_DEFINE_TYPE_INTRUSIVE but I am getting the error:
error: no matching function for call to
‘nlohmann::basic_json<>::get()’ 19 | game…
callum arul
- 159
- 6
2
votes
1 answer
Converting json file to json object jumbles up the order of objects
I am trying to parse a json file into a json object using nlohmann json library.
This is the json file:
{
"n":1,
"data":
{
"name":"Chrome",
"description":"Browse the internet.",
"isEnabled":true
}
}
This is…
callum arul
- 159
- 6
2
votes
1 answer
Change Nlohmann json key-value with increment function? c++
Instead of this:
j["skills"]["atk"] = j["skills"]["atk"].get() + 6;
I want something like this:
void json_inc(json ref, int value) //function to increment int key-values
{
ref = ref.get() + value;
}
json_inc(j["skills"]["atk"], 6);…
user19816087
- 79
- 5
2
votes
2 answers
Convert JSON to array with nlohmann/json
I've not used C++ in over 20 years, so I am a bit rusty on this.
I am using the nlohmann/json json.h library and need to convert a JSON string that is an array of objects to an actual array.
As an example, I need to take this kind of response from a…
Norm Strassner
- 225
- 3
- 11