toml11

c++11 header-only toml parser depending only on c++ standard library.

compatible to the latest version of TOML v0.5.0 after version 2.0.0.

Are you looking for pre-C++11 compatible toml parser? Check out Boost.toml! It has almost the same functionality as this library and work with C++98 & Boost.

How to use

installation

Just include the file after adding correct include path.

#include <toml11/toml.hpp> // that's all! now you can use it.

int main()
{
    const auto data  = toml::parse("example.toml");
    const auto title = toml::get<std::string>(data.at("title"));
    std::cout << "the title is " << title << std::endl;
}

decoding toml file

parsing toml file

The only thing you have to do is passing a filename to toml::parse function.

const std::string fname("sample.toml");
const toml::table data = toml::parse(fname);

In the case of file open error, it will throw std::runtime_error.

You can pass also stream to toml::parse function after checking the status.

std::ifstream ifs("sample.toml");
assert(ifs.good());
const auto data = toml::parse(ifs /*, "filename" (optional)*/);

To show a better error message, it is recommended to pass filename with istream. See also in the case of syntax error and passing invalid type to toml::get.

in the case of syntax error

If there is a syntax error in a toml file, toml::parse will throw toml::syntax_error.

toml11 now has clean error messages inspired the Rust compiler and it looks like the following (comment after hash sign are actually not shown).

terminate called after throwing an instance of 'toml::syntax_error'
  what():  [error] toml::parse_table: invalid line format # error description
 --> example.toml                                         # file name (and path, if any)
 3 | a = 42 = true                                        # line num and content
   |        ^------ expected newline, but got '='.        # error reason

It shows almost all the information to fix the error in the toml file like file name, line number, the line that is invalid, and the reason why it fails.

Since the error message generation is generally a difficult task, the current status is not ideal. We need your help. If you encounter a weird error message, please let us know and improve the quality!

getting toml value

After parsing successfully, you can obtain the values from the result of toml::parse (here, data) using toml::get function.

answer  = 42
pi      = 3.14
numbers = [1,2,3]
time    = 1979-05-27T07:32:00Z
[tab]
key = "value"

const auto answer    = toml::get<std::int64_t    >(data.at("answer"));
const auto pi        = toml::get<double          >(data.at("pi"));
const auto numbers   = toml::get<std::vector<int>>(data.at("numbers"));
const auto timepoint = toml::get<std::chrono::system_clock::time_point>(data.at("time"));
const auto tab       = toml::get<toml::Table>(data.at("tab"));
const auto key       = toml::get<std::string>( tab.at("key"));

When you pass an exact TOML type that does not require type conversion, toml::get returns also a reference through which you can modify the content.

toml::get<toml::integer>(data["answer"]) = 6 * 9;
std::cout << toml::get<int>(data.at("answer")) << std::endl; // 54

passing invalid type to toml::get

If you choose the invalid type, toml::type_error will be thrown. Similar to the syntax_error, toml11 also displays informative error message. The error message when you choose int to get string value would be like this.

terminate called after throwing an instance of 'toml::type_error'
  what():  [error] toml::value bad_cast to integer
 --> example.toml
 3 | title = "TOML Example"
   |         ~~~~~~~~~~~~~~ the actual type is string

NOTE: In order to show this kind of error message, all the toml values has 1 shared_ptr that points the corresponding byte sequence and 2 iterator that points the range. It is recommended to destruct all the toml::value classes after configuring your application to save the memory resource.

finding value from table

toml11 provides overloads to find a value from toml::table. Of course, you can do this in your own way with toml::get because it just searches and returns a value.

const auto data = toml::parse("example.toml");
const auto num  = toml::get<int>(data, "num", /*optional*/"example.toml");

If the value does not exists, it throws std::out_of_range with informative error message.

terminate called after throwing an instance of 'std::out_of_range'
  what():  [error] key "num" not found in example.toml

You can use this with a toml::value that is expected to be a toml::table. It automatically casts the value to table.

const auto data = toml::parse("example.toml");
const auto num  = toml::get<int>(data.at("table"), "num");
// expecting the following example.toml
// [table]
// num = 42

In this case, because the value data.at("table") knows the locatoin of itself, you don't need to pass where you find the value. toml::get will show you a great error message.

terminate called after throwing an instance of 'std::out_of_range'
  what():  [error] key "num" not found
 --> example.toml
 3 | [table]
   | ~~~~~~~ in this table

If it's not a toml::table, error like "invalid type" would be thrown.

getting arrays

You can set any kind of container class to obtain toml::array except for map-like classes.

const auto vc  = toml::get<std::vector<int>  >(data.at("numbers"));
const auto ls  = toml::get<std::list<int>    >(data.at("numbers"));
const auto dq  = toml::get<std::deque<int>   >(data.at("numbers"));
const auto ar  = toml::get<std::array<int, 3>>(data.at("numbers"));
// if the size of data.at("numbers") is larger than that of std::array,
// it will throw toml::type_error because std::array is not resizable.

Surprisingly, you can get toml::array as std::pair and std::tuple.

const auto tp = toml::get<std::tuple<short, int, unsigned int>>(data.at("numbers"));

The case when you need this functionality is to get an array of arrays.

aofa = [[1,2,3], ["foo", "bar", "baz"]] # toml allows this

What is the corresponding C++ type? Obviously, it is a std::pair of std::vectors.

const auto aofa = toml::get<
    std::pair<std::vector<int>, std::vector<std::string>>
    >(data.at("aofa"));

If you don't know what the type is inside the array, you can use toml::array which is a std::vector of toml::valueinstead.

const auto aofa  = toml::get<toml::array>(data.at("aofa"));
const auto first = toml::get<toml::array>(aofa.at(0));

See also expecting conversion and checking-value-type.

getting tables

toml::table is a key component of this library, that is an alias of a std::unordered_map from toml::key (a.k.a. std::string) to toml::value. toml::parse returns this as a result.

Since it is just an alias of std::unordered_map, it has all the functionalities that std::unordered_map has, e.g. operator[], count, and find.

toml::table data = toml::parse("example.toml");
if(data.count("title") != 0)
{
    data["title"] = std::string("TOML example");
}

For the case that all the values of the table have the same type, toml11 allows you to convert toml::table to maps that contains the convertible type.

[tab]
key1 = "foo" # all the values are
key2 = "bar" # toml String

const auto tab = toml::get<std::map<std::string, std::string>>(data.at("tab"));
std::cout << tab["key1"] << std::endl; // foo
std::cout << tab["key2"] << std::endl; // bar

dotted keys

TOML v0.5.0 has a new feature named "dotted keys". You can chain keys to represent the structure of the data.

physical.color = "orange"
physical.shape = "round"

This is equivalent to the following.

[physical]
color = "orange"
shape = "round"

You can get both of the above formats with the same c++ code.

const auto physical = toml::get<toml::table>(data.at("physical"));
const auto color    = toml::get<std::string>(physical.at("color"));

an array of tables

An array of tables is just an array of tables. You can get completely in the same way as the other arrays and tables.

array_of_inline_table = [{key = "value1"}, {key = "value2"}, {key = "value3"}]

[[array_of_table]]
key = "value4"
[[array_of_table]]
key = "value5"
[[array_of_table]]
key = "value6"

const auto aot1 = toml::get<std::vector<toml::table>>(data.at("array_of_inline_table"));
const auto aot2 = toml::get<std::vector<toml::table>>(data.at("array_of_table"));

cost of conversion

Although toml::get is convenient, it has additional copy-cost because it copies data contained in toml::value to user-specified type. Of course in some case this overhead is not ignorable.

By passing the exact types, toml::get returns reference that has nealy zero overhead.

const auto& tab     = toml::get<toml::array>(data.at("tab"));
const auto& numbers = toml::get<toml::table>(data.at("numbers"));

Unfortunately, in this case you need to call toml::get each time you access to the element of toml::array because toml::array is an array of toml::value.

const auto& num0 = toml::get<toml::integer>(numbers.at(0));
const auto& num1 = toml::get<toml::integer>(numbers.at(1));
const auto& num2 = toml::get<toml::integer>(numbers.at(2));

datetime and its variants

TOML v0.5.0 has 4 different datetime objects, local_date, local_time, local_datetime, and offset_datetime. With toml11, you can convert local_time to your favorite std::chrono::duration and others to std::chrono::system_clock::time_point.

time = 12:30:00
date = 2018-12-23

const auto dur = toml::get<std::chrono::minutes>(data.at("time")); // 12 * 60 + 30 min
const auto tp  = toml::get<std::chrono::system_clock::time_point>(data.at("date"));

getting with a fallback

toml::get_or returns a default value if toml::get<T> failed.

toml::table data; // empty table!
const auto value = toml::get_or(data, "key", 42); // value => int 42.

toml::get_or automatically deduces what type you want to get from the default value you passed.

expecting conversion

By using toml::expect, you will get your expected value or an error message without throwing toml::type_error.

const auto value = toml::expect<std::string>(data.at("title"));
if(value.is_ok()) {
    std::cout << value.unwrap() << std::endl;
} else {
    std::cout << value.unwrap_err() << std::endl;
}

Also, you can pass a function object to modify the expected value.

const auto value = toml::expect<int>(data.at("number"))
    .map(// function that receives expected type (here, int)
    [](const int number) -> double {
        return number * 1.5 + 1.0;
    }).unwrap_or(/*default value =*/ 3.14);

checking value type

When you don't know the exact type of toml-value, you can get enum type from toml::value.

switch(data.at("something").type())
{
    case toml::value_t::Integer: /* do some stuff */; break;
    case toml::value_t::Float  : /* do some stuff */; break;
    case toml::value_t::String : /* do some stuff */; break;
    default : throw std::runtime_error(
        "unexpected type : " + toml::stringize(data.at("something").type()));
}

fill only the matched value

The more sophisticated way is using toml::from_toml and std::tie.

toml::table data{{"something", toml::value("foo")}};
int         i = 0;
double      d = 0.;
std::string s;
toml::from_toml(std::tie(i, d, s), data.at("something"));
std::cout << i << ", " << d << ", " << s << std::endl; // 0, 0, foo

Here, only matched value will be filled. The others are left intact after calling from_toml. It should be noted that toml::from_toml returns as usual even if there are no matched type.

from_toml can be used also for single type.

int i = 0;
toml::from_toml(i, data.at("something"));

sanitizing UTF-8 codepoints

toml11 shows warning if a value of an escape sequence to represent unicode character exceeds the range of unicode.

[warning] input codepoint (0011FFFF) is too large to decode as a unicode character. The result may not be able to render to your screen.
 --> example.toml
 3 | exceeds_unicode = "\U0011FFFF example"
   |                     ~~~~~~~~~ should be in [0x00..0x10FFFF]

Also, toml11 throws std::domain_error if the code point exceeds the range that can be represented by utf-8.

terminate called after throwing an instance of 'std::range_error'
  what():  [error] input codepoint (0020FFFF) is too large to encode as utf-8.
 --> example.toml
 3 | exceeds_utf8    = "\U0020FFFF example"
   |                     ~~~~~~~~~ should be in [0x00..0x10FFFF]

underlying types

The toml types (can be used as toml::* in this library) and corresponding enum name are listed in the table below.

toml::type	underlying c++ type	enum
Boolean	bool	toml::value_t::Boolean
Integer	std::int64_t	toml::value_t::Integer
Float	double	toml::value_t::Float
String	toml::string	toml::value_t::String
LocalDate	toml::local_date	toml::value_t::LocalDate
LocalTime	toml::local_time	toml::value_t::LocalTime
LocalDatetime	toml::local_datetime	toml::value_t::LocalDatetime
OffsetDatetime	toml::offset_datetime	toml::value_t::offsetDatetime
Array	std::vector<toml::value>	toml::value_t::Array
Table	std::unordered_map<std::string, toml::key>	toml::value_t::Table

toml::string is effectively the same as std::string but has an additional flag that represents a kind of a string, string_t::basic and string_t::literal. Although std::string is not an exact toml type, but still you can get a reference that points internal std::string by using toml::get<std::string>() for the convenience.

Datetime variants are struct that are defined in this library. Because std::chrono::system_clock::time_point is a time point, not capable of representing a Local Time independent from a specific day.

It is recommended to get Datetimes as std::chrono classes through toml::get.

Contributors

I thank the contributor for providing great feature to this repository.

• Guillaume Fraux (@Luthaf)
  • Windows support and CI on Appvayor
  • Intel Compiler support

Licensing terms

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

• Copyright (c) 2017 Toru Niina

All rights reserved.