Niels Lohmann
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* Docs: fill documentation gaps found in user questions Add pages on class-hierarchy/smart-pointer/variant/chrono recipes, working without exceptions, and large, streamed and partial input. Extend the FAQ (23 entries, Known bugs first), parse error documentation (empty-input checklist, line/column, diagnostic positions), element access, conversions, creating values, ADL troubleshooting, memory, and build/distribution notes. Add 14 examples with generated output. Correct the statement that parse errors cannot be recovered from with -fno-exceptions. The topics come from recurring questions on Stack Overflow, Reddit, Hacker News, YouTube, and the project's GitHub discussions and issues. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * docs: declare range-for lists in variables to keep astyle quiet astyle reformats a braced init list placed directly in a range-for header; declare the list first so check_amalgamation passes. Signed-off-by: Niels Lohmann <mail@nlohmann.me> --------- Signed-off-by: Niels Lohmann <mail@nlohmann.me>
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JSON for Modern C++
JSON for Modern C++ is a header-only C++11 library that turns JSON into a first-class C++ data type, using the operator
magic of modern C++ so that creating, reading, and modifying JSON values feels as natural as it does in languages like
Python. The whole library is available as a single header, json.hpp, with no dependencies, no subproject, and no
complex build system to set up; a companion header, json_fwd.hpp, provides forward declarations to keep compile times
down, <nlohmann/json_literals.hpp> holds the user-defined string literals on their own, and
<nlohmann/json_view.hpp> adds zero-copy views and editable documents. See
header-only integration for details. It is heavily unit-tested with 100% code
coverage, checked with Valgrind and the Clang Sanitizers for memory leaks, and continuously fuzz-tested by Google
OSS-Fuzz.
Quick start
Add the single header to your project and use the library like this:
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
// parse a JSON string
json j = json::parse(R"({"happy": true, "pi": 3.141})");
// access and modify values
j["name"] = "Niels";
j["list"] = {1, 0, 2};
// read a value into a C++ variable and use it
double pi = j["pi"].get<double>();
std::cout << "2 * pi = " << 2 * pi << '\n';
// serialize with an indent of 4 spaces
std::cout << j.dump(4) << '\n';
}
Get the library by copying the single header json.hpp from the
releases page into a directory nlohmann on your include path, or by installing it with a package manager:
brew install nlohmann-json # Homebrew
vcpkg install nlohmann-json # vcpkg
find_package(nlohmann_json 3.12.0 REQUIRED)
target_link_libraries(myproject PRIVATE nlohmann_json::nlohmann_json)
See Integration for CMake in detail, all supported package managers (Conan, Meson, Bazel, Conda, and more), and pkg-config.
Explore the documentation
-
:octicons-rocket-24:{ .lg .middle } Features
Creating, parsing, accessing, and serializing JSON values, JSON Pointer/Patch, binary formats, zero-copy views, and more.
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:octicons-package-24:{ .lg .middle } Integration
Add the library to your project via a single header, CMake, a package manager, or pkg-config.
-
:octicons-book-24:{ .lg .middle } API documentation
The complete reference for
basic_jsonand its member functions, types, and related classes, as well as forjson_documentandjson_view. -
:octicons-question-24:{ .lg .middle } FAQ
Answers to common questions and known surprises when using the library.
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:octicons-tag-24:{ .lg .middle } Releases
What changed in each release, with links to the relevant documentation.
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:octicons-people-24:{ .lg .middle } Community
The ecosystem, contribution guidelines, governance, and quality assurance around the project.
!!! info "Unreleased changes"
This documentation is built from the `develop` branch and may describe changes that are not part of a release
yet. Their version numbers are followed by an <span class="unreleased-version">unreleased</span> badge; see
[Releases](home/releases/index.md) for what shipped in each version.
The library is licensed under the MIT License. The source code, issue tracker, and discussions are on GitHub.