toml11

C++11 header-only toml parser/encoder 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? Try Boost.toml! It has almost the same functionality as this library and works with C++98 & Boost.

How to use

Installation

Just include the file after adding it to the 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

The only thing you have to do is to pass a filename to the 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 also pass a stream to the toml::parse function after checking the status.

Note that on Windows OS, stream that is opened as text-mode automatically converts CRLF ("\r\n") into LF ("\n") and this leads inconsistency between file size and the contents that would be read. This causes weird error. To use a file stream with toml::parse, don't forget to pass binary mode flag when you open the stream.

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

To show a better error message, it is recommended to pass a 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 and informative error messages inspired by Rust 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
 3 | a = 42 = true                                        # line num and content
   |        ^------ expected newline, but got '='.        # error reason

If you (mistakenly) duplicate tables and got an error, you may want to see where the other is. toml11 shows both at the same time.

terminate called after throwing an instance of 'toml::syntax_error'
  what():  [error] toml::insert_value: table ("table") already exists.
 --> duplicate-table.toml
 1 | [table]
   | ~~~~~~~ table already exists here
 ...
 3 | [table]
   | ~~~~~~~ table defined twice

Since the error message generation is generally a difficult task, the current status is not ideal. toml11 needs your help. If you encounter a weird error message, please let us know and contribute to improve the quality!

Getting a 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

If the specified type requires conversion, you can't take a reference to the value. See also underlying types.

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 messages. 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 have 1 shared_ptr that points the corresponding byte sequence and 2 iterators that point the range. It is recommended to destruct all the toml::value classes after configuring your application to save memory resources.

Getting arrays

You can set any kind of container class to obtain a 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 also get a 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::value, instead.

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, which is an alias of a std::unordered_map from toml::key (a.k.a. std::string) to toml::value. toml::parse returns this.

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");
}

When all the values of the table have the same type, toml11 allows you to convert a toml::table to a map 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 it 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 the 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);

Finding value from table

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

const auto data = toml::parse("example.toml");
const auto num  = toml::find<int>(data, "num", /*for err msg*/"example.toml");

If the value does not exist, 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::find<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::find 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, the same error as "invalid type" would be thrown.

Checking value type

You can check what type of value does toml::value contains by is_* function.

toml::value v = /* ... */;
if(v.is_integer() && toml::get<int>(v) == 42)
{
    std::cout << "value is 42" << std::endl;
}

The complete list of the functions is below.

• bool toml::value::is_boolean() const noexcept;
• bool toml::value::is_integer() const noexcept;
• bool toml::value::is_float() const noexcept;
• bool toml::value::is_string() const noexcept;
• bool toml::value::is_offset_datetime() const noexcept;
• bool toml::value::is_local_datetime() const noexcept;
• bool toml::value::is_local_date() const noexcept;
• bool toml::value::is_local_time() const noexcept;
• bool toml::value::is_array() const noexcept;
• bool toml::value::is_table() const noexcept;
• bool toml::value::is_uninitialized() const noexcept;

Also, you can get enum class value 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()));
}

The complete list of the enums can be found in the section underlying types.

The enums can be used as a parameter of toml::value::is function like the following.

toml::value v = /* ... */;
if(v.is(toml::value_t::Boolean)) // ...

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"));

Conversion between toml value and your class

You can also use toml::get and other related functions with the types you defined after you implement some stuff.

namespace ext
{
struct foo
{
    int         a;
    double      b;
    std::string c;
};
} // ext

const auto data = toml::parse("example.toml");

const foo f = toml::get<ext::foo>(data.at("foo"));

There are 2 ways to use toml::get with the types that you defined.

The first one is to implement from_toml(const toml::value&) member function.

namespace ext
{
struct foo
{
    int         a;
    double      b;
    std::string c;

    void from_toml(const toml::value& v)
    {
        this->a = toml::find<int        >(v, "a");
        this->b = toml::find<double     >(v, "b");
        this->c = toml::find<std::string>(v, "c");
        return;
    }
};
} // ext

In this way, because toml::get first constructs foo without arguments, the type should be default-constructible.

The second is to implement specialization of toml::from for your type.

namespace ext
{
struct foo
{
    int         a;
    double      b;
    std::string c;
};
} // ext

namespace toml
{
template<>
struct from<ext::foo>
{
    ext::foo from_toml(const toml::value& v)
    {
        ext::foo f;
        f.a = toml::find<int        >(v, "a");
        f.b = toml::find<double     >(v, "b");
        f.c = toml::find<std::string>(v, "c");
        return f;
    }
};
} // toml

In this way, since the conversion function is introduced from out of the class, you can add conversion between toml::value and classes defined in another library.

Note that you cannot implement both of the functions because the overload resolution of toml::get become ambiguous.

---

The opposite direction is also supported in a similar way. You can directly pass your type to toml::value's constructor by introducing into_iter or toml::into<T>.

namespace ext
{
struct foo
{
    int         a;
    double      b;
    std::string c;

    toml::table into_toml() const // you need to mark it const.
    {
        return toml::table{{"a", this->a}, {"b", this->b}, {"c", this->c}};
    }
};
} // ext

ext::foo    f{42, 3.14, "foobar"};
toml::value v(f);

The definition of toml::into<ext::foo> is similar to from_toml().

namespace ext
{
struct foo
{
    int         a;
    double      b;
    std::string c;
};
} // ext

namespace toml
{
template<>
struct into<ext::foo>
{
    toml::table into_toml(const ext::foo& v)
    {
        return toml::table{{"a", this->a}, {"b", this->b}, {"c", this->c}};
    }
};
} // toml

ext::foo    f{42, 3.14, "foobar"};
toml::value v(f);

Any type that can be converted to toml::value, e.g. toml::table, toml::array, is okay to return from into_toml.

visiting toml::value

TOML v2.1.0+ provides toml::visit to apply a function to toml::value in the same way as std::variant.

const toml::value v(3.14);
toml::visit([](const auto& val) -> void {
        std::cout << val << std::endl;
    }, v);

The function object that would be passed to toml::visit must be able to recieve all the possible TOML types. Also, the result types should be the same each other.

Sanitizing UTF-8 codepoints

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

[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]

Formatting your error

When you encounter an error after you read the toml value, you may want to show the error with the value.

toml11 provides you a function that formats user-defined error message with related values. With a code like the following,

const auto value = toml::find<int>(data, "num");
if(value < 0)
{
    std::cerr << toml::format_error("[error] value should be positive",
                                    data.at("num"), "positive number required")
              << std::endl;
}

you will get an error message like this.

[error] value should be positive
 --> example.toml
 3 | num = -42
   |       ~~~ positive number required

When you pass two values to toml::format_error,

const auto min = toml::find<int>(range, "min");
const auto max = toml::find<int>(range, "max");
if(max < min)
{
    std::cerr << toml::format_error("[error] max should be larger than min",
                                    data.at("min"), "minimum number here",
                                    data.at("max"), "maximum number here");
              << std::endl;
}

you will get an error message like this.

[error] max should be larger than min
 --> example.toml
 3 | min = 54
   |       ~~ minimum number here
 ...
 4 | max = 42
   |       ~~ maximum number here

Serializing TOML data

toml11 v2.1.0 enables you to serialize data into toml format.

const auto data = toml::table{{"foo", 42}, {"bar", "baz"}};

const std::string serial = toml::format(data);
// serial == "{bar=\"baz\",foo=42}"

std::cout << data << std::endl;
// bar = "baz"
// foo = 42

toml11 automatically makes a tiny table and array inline. You can specify the width to make them inline by std::setw for streams.

const auto data = toml::table{
    {"qux",    toml::table{{"foo", 42}, {"bar", "baz"}}},
    {"quux",   toml::array{"small", "array", "of", "strings"}},
    {"foobar", toml::array{"this", "array", "of", "strings", "is", "too", "long",
                           "to", "print", "into", "single", "line", "isn't", "it?"}},
};

// the threshold becomes 80.
std::cout << std::setw(80) << data << std::endl;
// foobar = [
// "this","array","of","strings","is","too","long","to","print","into",
// "single","line","isn't","it?",
// ]
// quux = ["small","array","of","strings"]
// qux = {bar="baz",foo=42}


// the width is 0. nothing become inline.
std::cout << std::setw(0) << data << std::endl;
// foobar = [
// "this",
// ... (snip)
// "it?",
// ]
// quux = [
// "small",
// "array",
// "of",
// "strings",
// ]
// [qux]
// bar = "baz"
// foo = 42

It is recommended to set width before printing data. Some I/O functions changes width to 0, and it makes all the stuff (including toml::array) multiline. The resulting files becomes too long.

toml::format receives optional second argument to set the width. By default, it is 80.

const auto data = toml::table{
    {"qux", toml::table{{"foo", 42}, {"bar", "baz"}}}
};

const std::string serial = toml::format(data, /*width = */ 0);
// [qux]
// bar = "baz"
// foo = 42

To control the precision of floating point numbers, you need to pass std::setprecision to stream or pass int to the optional third argument of toml::format (by default, it is std::numeric_limits<double>::max_digit10).

const auto data = toml::table{
    {"pi", 3.141592653589793},
    {"e",  2.718281828459045}
};
std::cout << std::setprecision(17) << data << std::endl;
// e = 2.7182818284590451
// pi = 3.1415926535897931
std::cout << std::setprecision( 7) << data << std::endl;
// e = 2.718282
// pi = 3.141593

const std::string serial = toml::format(data, /*width = */ 0, /*prec = */ 17);

Underlying types

The toml types (can be used as toml::* in this library) and corresponding enum names 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<toml::key, toml::value>	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, still you can get a reference that points to internal std::string by using toml::get<std::string>() for 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
• Quentin Khan (@xaxousis)
  • Found & Fixed a bug around ODR
  • Improved error message to show the location where the parser fails

Licensing terms

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

• Copyright (c) 2017 Toru Niina

All rights reserved.