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
38
votes
2 answers
C++: Reading a json object from file with nlohmann json
I am using the nlohmann's json library to work with json objects in c++. Ultimately, I'd like to read a json object from a file, e.g. a simple object like this.
{
"happy": true,
"pi": 3.141
}
I'm not quite sure how to approach this. At…
user3515814
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- 13
20
votes
2 answers
C++ debug/print custom type with GDB : the case of nlohmann json library
I'm working on a project using nlohmann's json C++ implementation.
How can one easily explore nlohmann's JSON keys/vals in GDB ?
I tried to use this STL gdb wrapping since it provides helpers to explore standard C++ library structures that…
LoneWanderer
- 3,058
- 1
- 23
- 41
16
votes
2 answers
c++ nlohmann json - how to iterate / find a nested object
I am trying to iterate over a nested json, using nlohmann::json. My json object is below:
{
"one": 1,
"two": 2
"three": {
"three.one": 3.1
},
}
I am trying to iterate and /or find nested objects. But, it seems there is no…
Mopparthy Ravindranath
- 3,014
- 6
- 41
- 78
14
votes
3 answers
How to check if key present in nested json in c++ using nlohmann
I have a below json data:
{
"images": [
{
"candidates": [
{
"confidence": 0.80836,
"enrollment_timestamp": "20190613123728",
"face_id":…
S Andrew
- 5,592
- 27
- 115
- 237
14
votes
1 answer
Adding header-only dependencies with CMake
I have a simple project which requires three header-only libraries in order to compile: websocketpp, spdlog and nlohmann/json.
The project structure looks like this:
└── src
├── app
│ ├── CMakeLists.txt
│ ├── src
│ └── test
…
arnaudoff
- 686
- 8
- 20
13
votes
4 answers
How to convert a json object to a map with nlohmann::json?
For example, with nlohmann::json, I can do
map> m = { {"a", {1, 2}}, {"b", {2, 3}} };
json j = m;
But I cannot do
m = j;
Any way to convert a json object to a map with nlohmann::json?
user1899020
- 13,167
- 21
- 79
- 154
12
votes
1 answer
Use nlohmann json to unpack list of integers to a std::vector
I'm using nlohman::json.
It's awesome, but is there any way to unpack:
{
"my_list" : [1,2,3]
}
into a std:vector ?
I can't find any mention in the docs, and std::vector v = j["my_list"]; fails, as does…
P i
- 29,020
- 36
- 159
- 267
11
votes
1 answer
How do you get a JSON object from a string in nlohmann json?
I have a string that I would like to parse into a json, but _json doesn't seem to work every time.
#include
#include
using nlohmann::json;
int main()
{
// Works as expected
json first = "[\"nlohmann\",…
Bob Galbil
- 113
- 1
- 1
- 4
10
votes
2 answers
Detect with "JSON for Modern C++" library that integer doesn't fit into a specified type?
This code prints -1:
#include
#include
int main()
{
auto jsonText = "{ \"val\" : 4294967295 }";
auto json = nlohmann::json::parse(jsonText);
std::cout << json.at("val").get() << std::endl;
}
I would…
user10101
- 1,704
- 2
- 20
- 49
8
votes
1 answer
Template issue with nlohmann::json
Here's my code and the error, and below I'll show some code that works.
#include
#include
#include
using JSON = nlohmann::json;
using std::cout;
using std::endl;
using std::string;
template
Joseph Larson
- 8,530
- 1
- 19
- 36
8
votes
1 answer
How to iterate over a JSON in JSON for modern c++
I would like to iterate over each of entries in a json object, but I am getting one incomprehensible error after the other. How to correct the following example?
#include
#include
using json = nlohmann::json;
void…
mnr
- 604
- 2
- 7
- 15
7
votes
2 answers
How to iterate over the types of std::variant?
I have some variant using V = std::variant and a function with the prototype V parse(const json&). The function should try to parse all the types (e.g. A, B, then C) till the first success (and it should do it implicitly, for there will be…
Nestor
- 687
- 5
- 12
7
votes
1 answer
Prettify a JSON string in C++ from a .txt file
I'm currently working in C++, getting an HTTP response from a request that I write into a .txt file using ostream. This happens asynchronously and I don't want to change this.
Once the data is done being written, I want to read from the…
user7420144
- 95
- 1
- 2
- 8
6
votes
1 answer
nlohmann json, converting to and from nested structures
I'm using nlohmann json (JSON for modern C++) with an embedded project. The OS is Mongoose OS. Mongoose has a nice config system where config data is handled and laid out in the mos.yml file. This file, at build time, is converted to structures and…
Jim Archer
- 1,337
- 5
- 30
- 43
6
votes
1 answer
c++, JSON array parsing using nlohmann::json
In a json file imported into my c++ program there is such structure as:
{
"a":"1",
"ec":[
{
"a":"0x00",
"s":[
{"a":"0xA0"},
{"a":"0xA1"},
],
"b":"v1"
},
{
…
Amir-Mousavi
- 4,273
- 12
- 70
- 123