// __ _____ _____ _____
// __| | __| | | | JSON for Modern C++ (supporting code)
// | | |__ | | | | | | version 3.12.0
// |_____|_____|_____|_|___| https://github.com/nlohmann/json
//
// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
// SPDX-License-Identifier: MIT
#include "doctest_compatibility.h"
#include <nlohmann/json.hpp>
using nlohmann::json;
#ifdef JSON_TEST_NO_GLOBAL_UDLS
using namespace nlohmann::literals; // NOLINT(google-build-using-namespace)
#endif
#include <deque>
#include <forward_list>
#include <list>
#include <set>
#include <unordered_map>
#include <unordered_set>
#include <iostream>
#include <sstream>
#include <iomanip>
// local variable is initialized but not referenced
DOCTEST_MSVC_SUPPRESS_WARNING_PUSH
DOCTEST_MSVC_SUPPRESS_WARNING(4189)
TEST_CASE("README" * doctest::skip())
{
{
// redirect std::cout for the README file
auto* old_cout_buffer = std::cout.rdbuf();
std::ostringstream const new_stream;
std::cout.rdbuf(new_stream.rdbuf());
{
// create an empty structure (null)
json j;
// add a number that is stored as double (note the implicit conversion of j to an object)
j["pi"] = 3.141;
// add a Boolean that is stored as bool
j["happy"] = true;
// add a string that is stored as std::string
j["name"] = "Niels";
// add another null object by passing nullptr
j["nothing"] = nullptr;
// add an object inside the object
j["answer"]["everything"] = 42;
// add an array that is stored as std::vector (using an initializer list)
j["list"] = { 1, 0, 2 };
// add another object (using an initializer list of pairs)
j["object"] = { {"currency", "USD"}, {"value", 42.99} };
// instead, you could also write (which looks very similar to the JSON above)
json const j2 =
{
{"pi", 3.141},
{"happy", true},
{"name", "Niels"},
{"nothing", nullptr},
{
"answer", {
{"everything", 42}
}
},
{"list", {1, 0, 2}},
{
"object", {
{"currency", "USD"},
{"value", 42.99}
}
}
};
}
{
// ways to express the empty array []
json const empty_array_implicit = {{}};
CHECK(empty_array_implicit.is_array());
json const empty_array_explicit = json::array();
CHECK(empty_array_explicit.is_array());
// a way to express the empty object {}
json const empty_object_explicit = json::object();
CHECK(empty_object_explicit.is_object());
// a way to express an _array_ of key/value pairs [["currency", "USD"], ["value", 42.99]]
json array_not_object = json::array({ {"currency", "USD"}, {"value", 42.99} });
CHECK(array_not_object.is_array());
CHECK(array_not_object.size() == 2);
CHECK(array_not_object[0].is_array());
CHECK(array_not_object[1].is_array());
}
{
// create object from string literal
json const j = "{ \"happy\": true, \"pi\": 3.141 }"_json; // NOLINT(modernize-raw-string-literal)
// or even nicer with a raw string literal
auto j2 = R"({
"happy": true,
"pi": 3.141
})"_json;
// or explicitly
auto j3 = json::parse(R"({"happy": true, "pi": 3.141})");
// explicit conversion to string
std::string const s = j.dump(); // NOLINT(bugprone-unused-local-non-trivial-variable) // {\"happy\":true,\"pi\":3.141}
// serialization with pretty printing
// pass in the amount of spaces to indent
std::cout << j.dump(4) << std::endl; // NOLINT(performance-avoid-endl)
// {
// "happy": true,
// "pi": 3.141
// }
std::cout << std::setw(2) << j << std::endl; // NOLINT(performance-avoid-endl)
}
{
// create an array using push_back
json j;
j.push_back("foo");
j.push_back(1);
j.push_back(true);
// comparison
const bool x = (j == R"(["foo", 1, true])"_json); // true
CHECK(x == true);
// iterate the array
for (json::iterator it = j.begin(); it != j.end(); ++it) // NOLINT(modernize-loop-convert)
{
std::cout << *it << '\n';
}
// range-based for
for (auto& element : j)
{
std::cout << element << '\n';
}
// getter/setter
const auto tmp = j[0].get<std::string>(); // NOLINT(bugprone-unused-local-non-trivial-variable)
j[1] = 42;
const bool foo{j.at(2)};
CHECK(foo == true);
// other stuff
CHECK(j.size() == 3); // 3 entries
CHECK_FALSE(j.empty()); // false
CHECK(j.type() == json::value_t::array); // json::value_t::array
j.clear(); // the array is empty again
// create an object
json o;
o["foo"] = 23;
o["bar"] = false;
o["baz"] = 3.141;
// find an entry
CHECK(o.find("foo") != o.end());
if (o.find("foo") != o.end()) // NOLINT(readability-container-contains)
{
// there is an entry with key "foo"
}
}
{
std::vector<int> const c_vector {1, 2, 3, 4};
json const j_vec(c_vector);
// [1, 2, 3, 4]
std::deque<float> const c_deque {1.2f, 2.3f, 3.4f, 5.6f};
json const j_deque(c_deque);
// [1.2, 2.3, 3.4, 5.6]
std::list<bool> const c_list {true, true, false, true};
json const j_list(c_list);
// [true, true, false, true]
std::forward_list<int64_t> const c_flist {12345678909876, 23456789098765, 34567890987654, 45678909876543};
json const j_flist(c_flist);
// [12345678909876, 23456789098765, 34567890987654, 45678909876543]
std::array<unsigned long, 4> const c_array {{1, 2, 3, 4}};
json const j_array(c_array);
// [1, 2, 3, 4]
std::set<std::string> const c_set {"one", "two", "three", "four", "one"};
json const j_set(c_set); // only one entry for "one" is used
// ["four", "one", "three", "two"]
std::unordered_set<std::string> const c_uset {"one", "two", "three", "four", "one"};
json const j_uset(c_uset); // only one entry for "one" is used
// maybe ["two", "three", "four", "one"]
std::multiset<std::string> const c_mset {"one", "two", "one", "four"};
json const j_mset(c_mset); // both entries for "one" are used
// maybe ["one", "two", "one", "four"]
std::unordered_multiset<std::string> const c_umset {"one", "two", "one", "four"};
json const j_umset(c_umset); // both entries for "one" are used
// maybe ["one", "two", "one", "four"]
}
{
std::map<std::string, int> const c_map { {"one", 1}, {"two", 2}, {"three", 3} };
json const j_map(c_map);
// {"one": 1, "two": 2, "three": 3}
std::unordered_map<const char*, float> const c_umap { {"one", 1.2f}, {"two", 2.3f}, {"three", 3.4f} };
json const j_umap(c_umap);
// {"one": 1.2, "two": 2.3, "three": 3.4}
std::multimap<std::string, bool> const c_mmap { {"one", true}, {"two", true}, {"three", false}, {"three", true} };
json const j_mmap(c_mmap); // only one entry for key "three" is used
// maybe {"one": true, "two": true, "three": true}
std::unordered_multimap<std::string, bool> const c_ummap { {"one", true}, {"two", true}, {"three", false}, {"three", true} };
json const j_ummap(c_ummap); // only one entry for key "three" is used
// maybe {"one": true, "two": true, "three": true}
}
{
// strings
std::string const s1 = "Hello, world!";
json const js = s1;
auto s2 = js.get<std::string>(); // NOLINT(bugprone-unused-local-non-trivial-variable)
// Booleans
bool const b1 = true;
json const jb = b1;
const bool b2{jb};
CHECK(b2 == true);
// numbers
int const i = 42;
json const jn = i;
const double f{jn};
CHECK(f == 42);
// etc.
std::string const vs = js.get<std::string>(); // NOLINT(bugprone-unused-local-non-trivial-variable)
const bool vb = jb.get<bool>();
CHECK(vb == true);
const int vi = jn.get<int>();
CHECK(vi == 42);
// etc.
}
{
// a JSON value
json j_original = R"({
"baz": ["one", "two", "three"],
"foo": "bar"
})"_json;
// access members with a JSON pointer (RFC 6901)
j_original["/baz/1"_json_pointer];
// "two"
// a JSON patch (RFC 6902)
json const j_patch = R"([
{ "op": "replace", "path": "/baz", "value": "boo" },
{ "op": "add", "path": "/hello", "value": ["world"] },
{ "op": "remove", "path": "/foo"}
])"_json;
// apply the patch
json const j_result = j_original.patch(j_patch);
// {
// "baz": "boo",
// "hello": ["world"]
// }
// calculate a JSON patch from two JSON values
auto res = json::diff(j_result, j_original);
// [
// { "op":" replace", "path": "/baz", "value": ["one", "two", "three"] },
// { "op":"remove","path":"/hello" },
// { "op":"add","path":"/foo","value":"bar" }
// ]
}
// restore old std::cout
std::cout.rdbuf(old_cout_buffer);
}
}
DOCTEST_MSVC_SUPPRESS_WARNING_POP