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toml11 is a feature-rich TOML language library for C++11/14/17/20.

Example

#include <toml.hpp>
#include <iostream>

// ```toml
// title = "an example toml file"
// nums  = [3, 1, 4, 1, 5] # pi!
// ```

int main()
{
    // select TOML version at runtime (optional)
    auto data = toml::parse("example.toml", toml::spec::v(1,1,0));

    // find a value with the specified type from a table
    std::string title = toml::find<std::string>(data, "title");

    // convert the whole array into STL-like container automatically
    std::vector<int> nums = toml::find<std::vector<int>>(data, "nums");

    // access with STL-like manner
    if( ! data.contains("foo"))
    {
        data["foo"] = "bar";
    }
    if(data.at("nums").is_array())
    {
        data.push_back(9);
    }

    // check comments
    assert(data.at("nums").comments().at(0) == "# pi!");

    // pass a fallback
    std::string name = toml::find_or<std::string>(data, "name", "not found");

    // serialization considering format info
    data.at("nums").as_array_fmt().fmt = toml::array_format::multiline;
    data.at("nums").as_array_fmt().indent_type = toml::indent_char::space;
    data.at("nums").as_array_fmt().body_indent = 2;

    std::cout << toml::format(data) << std::endl;

    return 0;
}

For more details, please refer to the documentation.

Table of Contents

Integration

There are several ways to use toml11.

Here is a brief overview of each method. For more details, please refer to the documentation.

Single Include File

Copy single_include/toml.hpp to your preferred location and add it to your include path.

git submodule

By adding toml11 as a subdirectory using git submodule (or any other way), you can either add toml11/include to your include path or use add_subdirectory(toml11) in your CMake project.

CMake FetchContent

Using FetchContent, you can automatically download it.

include(FetchContent)
FetchContent_Declare(
  toml11
  GIT_REPOSITORY https://github.com/ToruNiina/toml11.git
  GIT_TAG        v4.1.0
)
FetchContent_MakeAvailable(toml11)

add_executable(main main.cpp)
target_link_libraries(main PRIVATE toml11::toml11)

CMake Package Manager (CPM)

After adding cpm to your project, you can use toml11 by doing:

include(cmake/CPM.cmake)

CPMAddPackage("gh:ToruNiina/toml11@4.1.0")

add_executable(main main.cpp)
target_link_libraries(main PUBLIC toml11::toml11)

Install Using CMake

You can install toml11 using CMake with the following steps:

$ git clone https://github.com/ToruNiina/toml11
$ cd toml11
$ git submodule update --init --recursive
$ cmake -B ./build/
$ cmake --build ./build/
$ cmake --install ./build/ --prefix /path/to/toml11

Precompile Library

By setting -DTOML11_PRECOMPILE=ON, you can precompile some of the library functions. In this case, the standard library features available will vary with the C++ version, and part of the interface will change. Therefore, you need to specify CMAKE_CXX_STANDARD.

$ cmake -B ./build/ -DTOML11_PRECOMPILE=ON -DCMAKE_CXX_STANDARD=11/14/17/20
$ cmake --build ./build/

When linking the library, use target_link_libraries in CMake

target_link_libraries(your_target PUBLIC toml11::toml11)

or pass -DTOML11_COMPILE_SOURCES to the compiler.

Building Example

To compile the examples in the examples/ directory, set -DTOML11_BUILD_EXAMPLES=ON.

$ cmake -B ./build/ -DTOML11_BUILD_EXAMPLES=ON
$ cmake --build ./build/

Building Tests

To compile unit tests, set -DTOML11_BUILD_TESTS=ON. Additionally, to compile the encoder and decoder for toml-test, set -DTOML11_BUILD_TOML_TESTS=ON.

$ cmake -B ./build/ -DTOML11_BUILD_EXAMPLES=ON
$ cmake --build ./build/

Features

Here is a brief overview of the features provided by toml11.

For more details, please refer to the documentation.

Parsing a File

To parse a file, use toml::parse.

The overall type of the file is always a table. However, since toml::value contains metadata such as comments and formatting information, toml::parse returns a toml::value rather than a toml::table.

const toml::value input = toml::parse("input.toml");

To parse a string directly, use toml::parse_str.

const toml::value input = toml::parse_str("a = 42");

When parsing string literals, you can use the ""_toml literal.

using namespace toml::literals::toml_literals;
const toml::value lit = "a = 42"_toml;

toml::parse, parse_str and _toml literal throw a toml::syntax_error exception in case of a syntax error.

The error message obtained with what() will look like this:

[error] bad integer: `_` must be surrounded by digits
 --> internal string at line 64 in file main.cpp
   |
 1 | a = 123__456
   |        ^-- invalid underscore
Hint: valid  : -42, 1_000, 1_2_3_4_5, 0xC0FFEE, 0b0010, 0o755
Hint: invalid: _42, 1__000, 0123

Error messages can also be colorized by calling toml::color::enable().

By using toml::try_parse, you can receive a toml::result<toml::value, std::vector<toml::error_info>> without throwing exceptions.

const auto input = toml::try_parse("input.toml");
if(input.is_ok())
{
    std::cout << input.unwrap().at("a").as_integer() << std::endl;
}

Additionally, toml11 allows easy and precise control over the version of the TOML language being used.

You can enable specific new features from TOML v1.1.0 while using TOML v1.0.0.

toml::spec s = toml::spec::v(1, 0, 0);
s.v1_1_0_allow_trailing_comma_in_inline_tables = true;

const toml::value input = toml::parse("input.toml");

Moreover, several language extensions not included in the TOML standard are available.

toml::spec s = toml::spec::v(1, 0, 0);
s.ext_hex_float  = true; // this allows hexadecimal floating-point numbers
s.ext_null_value = true; // this allows `key = null` value
s.ext_num_suffix = true; // this allows numeric suffixes like `100_msec`

For more detail and reference of each feature, please refer to the documentation.

finding a value

toml::value provides member functions for accessing values, such as at(), is_xxx(), and as_xxx().

const toml::value input = toml::parse("input.toml");
if(input.contains("a") && input.at("a").is_integer())
{
    std::cout << input.at("a").as_integer() << std::endl;
}

By using toml::find, you can perform type conversion and search simultaneously.

const toml::value input = toml::parse("input.toml");
std::cout << toml::find<int>(input, "a") << std::endl;

If type conversion or value lookup fails, a toml::type_error is thrown. The error message will look like this:

[error] toml::value::as_string(): bad_cast to string
 --> input.toml
   |
 1 | a = 123_456
   |     ^^^^^^^-- the actual type is integer

You can access nested tables or arrays of tables in the same way.

// [a]
// b = [
//   {c = 42},
//   {c = 54}
// ]
const toml::value input = toml::parse("input.toml");
std::cout << toml::find<int>(input, "a", "b", 1, "c") << std::endl;

Most STL containers and those with similar interfaces can be converted.

// array = [3,1,4,1,5]
const toml::value input = toml::parse("input.toml");

const auto a1 = toml::find<std::vector<int>>(input, "array");
const auto a2 = toml::find<std::array<int, 5>>(input, "array");
const auto a3 = toml::find<std::deque<int>>(input, "array");
const auto a4 = toml::find<boost::container::small_vector<int, 8>>(input, "array");

You can perform advanced type conversions on complex TOML values.

mixed_array = [
    42,
    3.14,
    {a = "foo", b = "bar"}
]

const toml::value input = toml::parse("input.toml");

const auto mixed = toml::find<
        std::tuple<int, double, std::map<std::string, std::string>>
    >(input, "mixed_array") << std::endl;

User-defined types can also be converted by using macros or defining some specific functions.

namespace extlib
{
struct foo
{
    int a;
    std::string b;
};
} // extlib
TOML11_DEFINE_CONVERSION_NON_INTRUSIVE(extlib::foo, a, b)

// ...

const auto input = R"(
  [foo]
  a = 42
  b = "bar"
)"_toml;
const extlib::foo f = toml::find<extlib::foo>(input, "foo");

Using toml::find_or, you can get a default value in case of failure.

const toml::value input = toml::parse("input.toml");
std::cout << toml::find_or(input, "a", 6*9) << std::endl;

For more details, please refer to the documentation.

comments

toml11 stores comments related to values within the value itself.

Comments related to a value include a series of comments written immediately before the value and any comments written after the value without a newline in between.

# This is a comment for a.
# This is also a comment for a.
a = 42 # This is also a comment for a.

# This is separated by a newline, so it is not a comment for b.

# This is a comment for b.
b = "foo"

These comments are stored in toml::value with an interface similar to std::vector<std::string>.

const toml::value input = toml::parse("input.toml");
std::cout << input.at("a").comments().size() << std::endl;
std::cout << input.at("a").comments().at(0) << std::endl;

For more details, please refer to the documentation.

error messages

One of the goals of toml11 is to provide clear and understandable error messages.

For parsing errors, you might see an error message like the following:

[error] bad integer: `_` must be surrounded by digits
 --> internal string at line 64 in file main.cpp
   |
 1 | a = 123__456
   |        ^-- invalid underscore
Hint: valid  : -42, 1_000, 1_2_3_4_5, 0xC0FFEE, 0b0010, 0o755
Hint: invalid: _42, 1__000, 0123

If you request a type different from the actual stored type, an error message like this will be displayed:

[error] toml::value::as_string(): bad_cast to string
 --> input.toml
   |
 1 | a = 123_456
   |     ^^^^^^^-- the actual type is integer

Such error messages can also be produced for user-specific algorithm that is not related to TOML syntax.

const toml::value& a = input.at("a");
if(a.as_integer() < 0)
{
    const toml::error_info err = toml::make_error_info(
            "positive integer is required",
            a, "but got negative value"
        );
    std::cerr << toml::format_error(err) << std::endl;
}

For more details, please refer to the documentation.

serialization

You can format a toml::value into a std::string using toml::format.

const toml::value input = toml::parse("input.toml");
std::cout << toml::format(input) << std::endl;

toml::format references the formatting information, allowing you to change the formatting method.

toml::value output(toml::table{ {"a", 0xDEADBEEF} });
output.at("a").as_integer_fmt().fmt = toml::integer_format::hex;
output.at("a").as_integer_fmt().spacer = 4; // position of `_`

std::cout << toml::format(input) << std::endl;
// a = 0xdead_beef

You can also specify the formatting for tables and arrays.

toml::value output(toml::table{
  {"array-of-tables", toml::array{}},
  {"subtable", toml::table{}},
});

auto& aot = output.at("array-of-tables");
aot.as_array_fmt().fmt = toml::array_format::multiline; // one element per line
aot.as_array_fmt().body_indent    = 4;
aot.as_array_fmt().closing_indent = 2;

toml::value v1(toml::table{ {"a", 42}, {"b", 3.14} });
v1.as_table_fmt().fmt = toml::table_format::oneline;
aot.push_back(std::move(v1));

toml::value v2(toml::table{ {"a", 42}, {"b", 3.14} });
v2.as_table_fmt().fmt = toml::table_format::oneline;
aot.push_back(std::move(v2));

output.at("subtable").as_table_fmt().fmt = toml::table_format::dotted;
output.at("subtable")["a"] = 42;
output.at("subtable")["b"] = 3.14;

std::cout << toml::format(output) << std::endl;
// subtable.b = 3.14
// subtable.a = 42
// array-of-tables = [
//     {b = 3.14, a = 42},
//     {b = 3.14, a = 42},
//   ]

These settings are read during parsing and will be maintained as long as the value type does not change when modified.

For details on possible formatting specifications, please refer to the documentation.

Configuring Types

Many types in toml::value, such as integer_type, array_type, table_type, etc, can be modified by changing the type_config type.

One commonly used example is an ordered_map that keeps the added order. toml11 provides atype_config that changes table_type to ordered_map as toml::ordered_type_config.

const toml::ordered_value input = toml::parse<toml::ordered_type_config>("input.toml");

Here, toml::ordered_value is an alias of toml::basic_value<toml::ordered_type_config>.

Note that, since toml::value uses std::unordered_map, once you convert it to toml::value, then the order of the values will be randomized.

For more details about how to implement type_config variant, please refer to the documentation.

Also, refer to the examples directory for complex use cases such as using multi-precision integers, changing containers, and normalizing Unicode. Use these examples as references for implementing such configurations.

Examples

The examples directory provides various implementation examples in addition to type configurations.

Changes from v3

toml11 v4 introduces several breaking changes.

Efforts have been made to minimize the need for changes for those using simple functionality. However, if you were utilizing advanced features, some adjustments may be necessary.

Nevertheless, we believe that the added or streamlined features will provide enhanced convenience in return.

Breaking Changes

Added features

Contributors

I appreciate the help of the contributors who introduced the great feature to this library.

Licensing terms

This product is licensed under the terms of the MIT License.

All rights reserved.