toml++ (tomlplusplus)

toml++ is a header-only toml parser and serializer for C++17, C++20 and whatever comes after.

• TOML v0.5.0, plus support for some unreleased TOML features (these are optional)
• C++17 (plus some C++20 features where available, e.g. experimental support for char8_t strings)
• Proper UTF-8 handling (incl. BOM)
• Works with or without exceptions
• Doesn't require RTTI
• First-class support for serializing to JSON

Example

Given a TOML file configuration.toml containing the following:

[library]
name = "toml++"
version = "0.1.0"
authors = ["Mark Gillard <mark@notarealwebsite.com>"]

[dependencies]
cpp = 17

Reading it in C++ is easy with toml++:

auto config = toml::parse_file( "configuration.toml" );

// get key-value pairs
std::string_view library_name = config["library"]["name"].value_or(""sv);
std::string_view library_version = config["library"]["version"].value_or(""sv);
std::string_view library_author = config["library"]["authors"][0].value_or(""sv);
int64_t depends_on_cpp_version = config["dependencies"]["cpp"].value_or(0);

// modify the data
config.insert_or_assign("alternatives", toml::array{
    "cpptoml",
    "toml11",
    "Boost.TOML"
});

// iterate & visit over the data
for (auto [k, v] : config)
{
    v.visit([](auto& node) noexcept
    {
        std::cout << node << std:endl;
        if constexpr (toml::is_string<decltype(node)>)
            do_something_with_string_values(node);
    });
}

// re-serialize as TOML
std::cout << config << std::endl;

// re-serialize as JSON
std::cout << toml::json_formatter{ config } << std::endl;

You'll find some more code examples in the examples directory, and plenty more as part of the API documentation.

Adding toml++ to your project

toml++ comes in two flavours: Regular and Single-header.

Regular mode

1. Add tomlplusplus/include to your include paths
2. #include <toml++/toml.h>

Single-header mode

1. Drop toml.hpp wherever you like in your source tree
2. There is no step two

The API is the same regardless of how you consume the library.

Configuration

A number of configurable options are exposed in the form of preprocessor #defines. Most likely you won't need to mess with these at all, butif you do, set them before including toml++.

Option	Type	Default	Description
TOML_ASSERT(expr)	function macro	assert(expr) (or undefined)	Sets the assert function used by the library.
TOML_CHAR_8_STRINGS	boolean	0	Uses C++20 char8_t-based strings as the toml string data type. Experimental!
TOML_CONFIG_HEADER	string literal	undefined	Includes the given header file before the rest of the library.
TOML_LARGE_FILES	boolean	0	Uses 32-bit integers for line and column indices (instead of 16-bit).
TOML_SMALL_FLOAT_TYPE	type name	undefined	If your codebase has an additional 'small' float type (e.g. half-precision), this tells toml++ about it.
TOML_SMALL_INT_TYPE	type name	undefined	If your codebase has an additional 'small' integer type (e.g. 24-bits), this tells toml++ about it.
TOML_UNDEF_MACROS	boolean	1	#undefs the library's internal macros at the end of the header.
TOML_UNRELEASED_FEATURES	boolean	1	Enables support for unreleased TOML language features not yet part of a numbered version.

TOML Language Support

At any given time toml++ aims to implement whatever the numbered version of TOML is, with the addition of unreleased features from the TOML master and some sane cherry-picks from the TOML issues list where the discussion strongly indicates inclusion in a near-future release.

The library advertises the most recent numbered language version it fully supports via the preprocessor defines TOML_LANG_MAJOR, TOML_LANG_MINOR and TOML_LANG_PATCH.

🔸Unreleased TOML features:

• #356: Allow leading zeros in the exponent part of a float
• #516: Allow newlines and trailing commas in inline tables
• #562: Allow hex floatingpoint values
• #567: Clarify that control characters are not permitted in comments
• #571: Allow raw tabs inside strings
• #644: Support + in key names
• #665: Make arrays heterogeneous
• #671: Local time of day format should support 09:30 as opposed to 09:30:00
• #687: Relax bare key restrictions to allow additional unicode characters

These can be disabled (and thus strict TOML v0.5.0 compliance enforced) by specifying TOML_UNRELEASED_FEATURES = 0 (see Configuration).

🔹TOML v0.5.0 and earlier:

• All features supported.

Contributing

Contributions are welcome, either by reporting issues or submitting pull requests. If you wish to submit a PR, please be aware that:

• The single-header file toml.hpp is generated by a script; make your changes in the files in include, not in toml.hpp.
• Your changes should compile warning-free on at least one of gcc 8.3.0, clang 8.0, and MSVC 19.2X (Visual Studio 2019). All three is a bonus.
• You should regenerate the single-header file as part of your PR (a CI check will fail if you don't).

Regenerating toml.hpp

1. Make your changes as necessary
2. If you've added a new header file that isn't going to be transitively included by one of the others, add an include directive to include/toml++/toml.h
3. Run python/generate_single_header.py

Building and testing

Testing is done using Catch2, included in the respository as a submodule under extern/Catch2. The first time you want to begin testing you'll need to ensure submodules have been fetched:

git submodule update --init --recursive extern/Catch2

Windows

Install Visual Studio 2019 and Test Adapter for Catch2, then open vs/toml++.sln and build the projects in the tests solution folder. Visual Studio's Test Explorer should pick these up and allow you to run the tests directly.

If test discovery fails you can usually fix it by clicking enabling Auto Detect runsettings Files (settings gear icon > Configure Run Settings).

Linux

Install meson and ninja if necessary, then test with both gcc and clang:

CXX=g++ meson build-gcc
CXX=clang++ meson build-clang
cd build-gcc && ninja && ninja test
cd ../build-clang && ninja && ninja test

License and Attribution

toml++ is licensed under the terms of the MIT license - see LICENSE.

UTF-8 decoding is performed using a state machine based on Bjoern Hoehrmann's 'Flexible and Economical UTF-8 Decoder', which is also subject to the terms of the MIT license - see LICENSE-utf8-decoder.