Parsing files

Call toml::parse_file() and work with the toml::table you get back, or handle any toml::parse_error that gets thrown:

#include <iostream>
#include <toml++/toml.h>

int main(int argc, char** argv)
{
   toml::table tbl;
   try
   {
       tbl = toml::parse_file(argv[1]);
           std::cout << tbl << "\n";
   }
   catch (const toml::parse_error& err)
   {
       std::cerr << "Parsing failed:\n" << err << "\n";
       return 1;
   }

   return 0;
}

Parsing strings and iostreams

Call toml::parse() and work with the toml::table you get back, or handle any toml::parse_error that gets thrown:

Try this code on Compiler Explorer
#include <iostream>
#include <sstream>
#include <toml++/toml.h>
using namespace std::string_view_literals;

int main()
{
   static constexpr std::string_view some_toml = R"(
       [library]
       name = "toml++"
       authors = ["Mark Gillard <mark.gillard@outlook.com.au>"]
       cpp = 17
   )"sv;

   try
   {
       // parse directly from a string view:
       {
           toml::table tbl = toml::parse(some_toml);
           std::cout << tbl << "\n";
       }

       // parse from a string stream:
       {
           std::stringstream ss{ std::string{ some_toml } };
           toml::table tbl = toml::parse(ss);
           std::cout << tbl << "\n";
       }
   }
   catch (const toml::parse_error& err)
   {
       std::cerr << "Parsing failed:\n" << err << "\n";
       return 1;
   }

   return 0;
}

[library]
authors = [ 'Mark Gillard <mark.gillard@outlook.com.au>' ]
cpp = 17
name = 'toml++'

[library]
authors = [ 'Mark Gillard <mark.gillard@outlook.com.au>' ]
cpp = 17
name = 'toml++'

Handling errors without exceptions

Can't (or won't) use exceptions? That's fine too. You can disable exceptions in your compiler flags and/or explicitly disable the library's use of them by setting the option TOML_EXCEPTIONS to 0. In either case, the parsing functions return a toml::parse_result instead of a toml::table:

#include <iostream>

#define TOML_EXCEPTIONS 0 // only necessary if you've left them enabled in your compiler
#include <toml++/toml.h>

int main()
{
   toml::parse_result result = toml::parse_file("configuration.toml");
   if (!result)
   {
       std::cerr << "Parsing failed:\n" << result.error() << "\n";
       return 1;
   }

   do_stuff_with_your_config(std::move(result).table()); // 'steal' the table from the result
   return 0;
}

Custom error formatting

The examples above use an overloaded operator<< with ostreams to print basic error messages, and look like this:

Error while parsing key: expected bare key starting character or string delimiter, saw '?'
    (error occurred at line 2, column 5)

In order to keep the library as small as possible I haven't bent over backwards to support things like custom colouring of the text in TTY environments, et cetera. That being said, the library provides the requisite information for you to build these yourself if necessary via toml::parse_error's source() and description() members:

toml::table tbl;
try
{
   tbl = toml::parse_file("configuration.toml");
}
catch (const toml::parse_error& err)
{
   std::cerr
       << "Error parsing file '" << *err.source().path
       << "':\n" << err.description()
       << "\n  (" << err.source().begin << ")\n";
   return 1;
}

Working with TOML data

A TOML document is a tree of values, arrays and tables, represented as the toml::value, toml::array and toml::table, respectively. All three inherit from toml::node, and can be easily accessed via the toml::node_view:

Try this code on Compiler Explorer
#include <iostream>
#include <toml++/toml.h>
using namespace std::string_view_literals;

int main()
{
   static constexpr auto source = R"(
       str = "hello world"

       numbers = [ 1, 2, 3, "four", 5.0 ]
       vegetables = [ "tomato", "onion", "mushroom", "lettuce" ]
       minerals = [ "quartz", "iron", "copper", "diamond" ]

       [animals]
       cats = [ "tiger", "lion", "puma" ]
       birds = [ "macaw", "pigeon", "canary" ]
       fish = [ "salmon", "trout", "carp" ]

   )"sv;
   toml::table tbl = toml::parse(source);

   // different ways of directly querying data
   std::optional<std::string_view> str1 = tbl["str"].value<std::string_view>();
   std::optional<std::string>      str2 = tbl["str"].value<std::string>();
   std::string_view                str3 = tbl["str"].value_or(""sv);
   std::string&                    str4 = tbl["str"].ref<std::string>(); // ~~dangerous~~

   std::cout << *str1 << "\n";
   std::cout << *str2 << "\n";
   std::cout << str3 << "\n";
   std::cout << str4 << "\n";

   // get a toml::node_view of the element 'numbers' using operator[]
   auto numbers = tbl["numbers"];
   std::cout << "table has 'numbers': " << !!numbers << "\n";
   std::cout << "numbers is an: " << numbers.type() << "\n";
   std::cout << "numbers: " << numbers << "\n";

   // get the underlying array object to do some more advanced stuff
   if (toml::array* arr = numbers.as_array())
   {
       for (toml::node& elem : *arr)
       {
           // visitation helps deal with the polymorphic nature of TOML data
           elem.visit([](auto&& el) noexcept
           {
               if constexpr (toml::is_number<decltype(el)>)
                   (*el)++;
               else if constexpr (toml::is_string<decltype(el)>)
                   el = "five"sv;
           });
       }

       // arrays are very similar to std::vector
       arr->push_back(7);
       arr->emplace_back<toml::array>(8, 9);
       std::cout << "numbers: " << numbers << "\n";
   }

   // node-views can be chained to quickly query deeper
   std::cout << "cats: " << tbl["animals"]["cats"] << "\n";
   std::cout << "fish[1]: " << tbl["animals"]["fish"][1] << "\n";

   // ...even if the element doesn't exist
   std::cout << "dinosaurs: " << tbl["animals"]["dinosaurs"] << "\n"; //no dinosaurs :(

   return 0;
}

hello world
hello world
hello world
hello world
table has 'numbers': 1
numbers is an: array
numbers: [ 1, 2, 3, 'four', 5.0 ]
numbers: [ 2, 3, 4, 'five', 6.0, 7, [ 8, 9 ] ]
cats: [ 'tiger', 'lion', 'puma' ]
fish[1]: 'trout'
dinosaurs:

Serializing as TOML and JSON

All toml++ data types have overloaded operator<< for ostreams, so 'serializing' a set of TOML data to actual TOML is done just by printing it to an ostream. Converting it to JSON is done in the same way, but via a toml::json_formatter.

Try this code on Compiler Explorer
#include <iostream>
#include <toml++/toml.h>

int main()
{
   auto tbl = toml::table{{
       { "lib", "toml++" },
       { "cpp", toml::array{ 17, 20, "and beyond" } },
       { "toml", toml::array{ "1.0.0", "and beyond" } },
       { "repo", "https://github.com/marzer/tomlplusplus/" },
       { "author", toml::table{{
               { "name", "Mark Gillard" },
               { "github", "https://github.com/marzer" },
               { "twitter", "https://twitter.com/marzer8789" }
           }}
       },
   }};

   // serializing as TOML
   std::cout << "###### TOML ######" << "\n\n";
   std::cout << tbl << "\n\n";

   // serializing as JSON using toml::json_formatter:
   std::cout << "###### JSON ######" << "\n\n";
   std::cout << toml::json_formatter{ tbl } << "\n\n";
   return 0;
}

###### TOML ######

cpp = [ 17, 20, 'and beyond' ]
lib = 'toml++'
repo = 'https://github.com/marzer/tomlplusplus/'
toml = [ '1.0.0', 'and beyond' ]

[author]
github = 'https://github.com/marzer'
name = 'Mark Gillard'
twitter = 'https://twitter.com/marzer8789'

###### JSON ######

{
    "author" : {
        "github" : "https://github.com/marzer",
        "name" : "Mark Gillard",
        "twitter" : "https://twitter.com/marzer8789"
    },
    "cpp" : [
        17,
        20,
        "and beyond"
    ],
    "lib" : "toml++",
    "repo" : "https://github.com/marzer/tomlplusplus/",
    "toml" : [
        "1.0.0",
        "and beyond"
    ]
}

Speeding up compilation

Because toml++ is a header-only library of nontrivial size you might find that compilation times noticeably increase after you add it to your project, especially if you add the library's header somewhere that's visible from a large number of translation units. You can counter this by disabling header-only mode and explicitly controlling where the library's implementation is compiled.

Step 1: Set TOML_HEADER_ONLY to 0 before including toml++

This must be the same everywhere, so either set it as a global #define in your build system, or do it manually before including toml++ in some global header that's used everywhere in your project:

// global_header_that_includes_toml++.h

#define TOML_HEADER_ONLY 0
#include <toml.hpp>

Step 2: Define TOML_IMPLEMENTATION before including toml++ in one specific translation unit

// some_code_file.cpp

#define TOML_IMPLEMENTATION
#include "global_header_that_includes_toml++.h"

Bonus Step: Disable the parser if you don't need it

If all you need to do is serialize some code-generated TOML and don't actually need the parser at all you can set TOML_PARSER to 0 to disable the parser altogether. This can yield fairly significant compilation speedups since the parser accounts for a good chunk of the library's code.

"The old fashioned way"

Clone the repository from GitHub, and then:

🍦️ Single-header flavour

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

🍨️ Regular flavour

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

Conan

Add tomlplusplus/2.5.0 to your conanfile.

DDS

Add tomlpp to your package.json5, e.g.:

depends: [
       'tomlpp^2.5.0',
]

Meson

The library supports being added as a subproject in the meson build system.

Vcpkg

vcpkg install tomlplusplus

CMake FetchContent

include(FetchContent)
FetchContent_Declare(
    tomlplusplus
    GIT_REPOSITORY https://github.com/marzer/tomlplusplus.git
    GIT_TAG        v2.5.0
)
FetchContent_MakeAvailable(tomlplusplus)

Other environments and package managers

toml++ is a fairly new project and I'm not up-to-speed with all of the available packaging and integration options in the modern C++ ecosystem. I'm also a cmake novice, for better or worse. If there's an integration option missing be assured that I fully support it being added, and welcome pull requests!

Special mention: Python

There exists a python wrapper library built around toml++ called pytomlpp which is, at the time of writing, the only natively-compiled TOML library available for python, and thus much faster than many of the alternatives:

Parsing data.toml 5000 times:
 pytomlpp:    0.662 s
     toml:    5.277 s (7.9x slower)
    qtoml:    8.020 s (12.1x slower)
  tomlkit:   32.898 s (49.6x slower)

Install it using pip:

pip install pytomlpp

Note that I'm not the owner of that project so if you wish to report a bug relating to the python implementation, please do so at their repository, not on the main toml++ one.