# stduuid
A C++17 cross-platform single-header library implementation **for universally unique identifiers**, simply know as either UUID or GUID (mostly on Windows). A UUID is a 128-bit number used to uniquely identify information in computer systems, such as database table keys, COM interfaces, classes and type libraries, and many others.

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For information about UUID/GUIDs see:
* [Universally unique identifier](https://en.wikipedia.org/wiki/Universally_unique_identifier)
* [A Universally Unique IDentifier (UUID) URN Namespace](https://www.ietf.org/rfc/rfc4122.txt)

## Library overview
Although the specification puts the uuid library in the `std` namespace, this implementation uses the namespace `uuids` for this purpose, in order to make the library usable without violating the restrictions imposed on the `std` namespace. The following types and utilities are available:

Basic types:

| Name | Description |
| ---- | ----------- |
| `uuid` | a class representing a UUID; this can be default constructed (a nil UUID), constructed from a range (defined by a pair of iterators), or from a `span`. |
| `uuid_variant` | a strongly type enum representing the type of a UUID |
| `uuid_version` | a strongly type enum representing the version of a UUID |

Generators:

| Name | Description |
| ---- | ----------- |
| `basic_uuid_random_generator` | a function object that generates version 4 UUIDs using a pseudo-random number generator engine. |
| `uuid_random_generator` | a `basic_uuid_random_generator` using the Marsenne Twister engine (`basic_uuid_random_generator<std::mt19937>`) |
| `uuid_name_generator` | a function object that generates version 5, name-based UUIDs using SHA1 hashing. |
| `uuid_system_generator` | a function object that generates new UUIDs using operating system resources (`CoCreateGuid` on Windows, `uuid_generate` on Linux, `CFUUIDCreate` on Mac) <br><br> **Note**: This is not part of the standard proposal. It is available only if the `UUID_SYSTEM_GENERATOR` macro is defined. |

Utilities:

| Name | Description |
| ---- | ----------- |
| `std::swap<>` | specialization of `swap` for `uuid` |
| `std::hash<>` | specialization of `hash` for `uuid` (necessary for storing UUIDs in unordered associative containers, such as `std::unordered_set`) |

Constants: 

| Name | Description |
| ---- | ----------- |
| `uuid_namespace_dns` | Namespace ID for name-based uuids when name string is a fully-qualified domain name. |
| `uuid_namespace_url` | Namespace ID for name-based uuids when name string is a URL. |
| `uuid_namespace_oid` | Namespace ID for name-based uuids when mame string is an ISO OID (See https://oidref.com/, https://en.wikipedia.org/wiki/Object_identifier). |
| `uuid_namespace_x500` | Namespace ID for name-based uuids when name string is an X.500 DN, in DER or a text output format (See https://en.wikipedia.org/wiki/X.500, https://en.wikipedia.org/wiki/Abstract_Syntax_Notation_One). |

Other:

| Name | Description |
| ---- | ----------- |
| `operator==` and `operator!=` | for UUIDs comparison for equality/inequality |
| `operator<` | for comparing whether one UUIDs is less than another. Although this operation does not make much logical sense, it is necessary in order to store UUIDs in a std::set. |
| `operator<<` | to write a UUID to an output stream using the canonical textual representation. |
| `to_string()` | creates a string with the canonical textual representation of a UUID. |

## Library history
This library is an implementation of the proposal [P0959](P0959.md).

**As the proposal evolves based on the standard committee and the C++ community feedback, this library implementation will reflect those changes.** 

See the revision history of the proposal for history of changes.

## Using the library
The following is a list of examples for using the library:
* Creating a nil UUID

  ```cpp
  uuid empty;
  assert(empty.is_nil());
  ```

* Creating a new UUID

  ```cpp
  uuid const id = uuids::uuid_system_generator{}();
  assert(!id.is_nil());
  assert(id.version() == uuids::uuid_version::random_number_based);
  assert(id.variant() == uuids::uuid_variant::rfc);
  ```

* Creating a new UUID with a default random generator

  ```cpp
  std::random_device rd;
  auto seed_data = std::array<int, std::mt19937::state_size> {};
  std::generate(std::begin(seed_data), std::end(seed_data), std::ref(rd));
  std::seed_seq seq(std::begin(seed_data), std::end(seed_data));
  std::mt19937 generator(seq);
  uuid const guid = uuids::uuid_random_generator{generator}();

  uuid const id = gen();
  assert(!id.is_nil());
  assert(id.size() == 16);
  assert(id.version() == uuids::uuid_version::random_number_based);
  assert(id.variant() == uuids::uuid_variant::rfc);
  ```

* Creating a new UUID with a particular random generator

  ```cpp
  std::random_device rd;
  auto seed_data = std::array<int, 6> {};
  std::generate(std::begin(seed_data), std::end(seed_data), std::ref(rd));
  std::seed_seq seq(std::begin(seed_data), std::end(seed_data));
  std::ranlux48_base generator(seq);

  uuids::basic_uuid_random_generator<std::ranlux48_base> gen(&generator);
  uuid const id = gen();
  assert(!id.is_nil());
  assert(id.size() == 16);
  assert(id.version() == uuids::uuid_version::random_number_based);
  assert(id.variant() == uuids::uuid_variant::rfc);
  ```

* Creating a new UUID with the name generator

  ```cpp
  uuids::uuid_name_generator gen(uuids::uuid::from_string("47183823-2574-4bfd-b411-99ed177d3e43").value());
  uuid const id = gen();

  assert(!id.is_nil());
  assert(id.version() == uuids::uuid_version::name_based_sha1);
  assert(id.variant() == uuids::uuid_variant::rfc);
  ```

* Create a UUID from a string

  ```cpp
  using namespace std::string_literals;

  auto str = "47183823-2574-4bfd-b411-99ed177d3e43"s;
  auto id = uuids::uuid::from_string(str);
  assert(id.has_value());
  assert(uuids::to_string(id.value()) == str);

  // or

  uuid id = uuids::uuid::from_string(L"{47183823-2574-4bfd-b411-99ed177d3e43}"s).value();
  assert(uuids::to_string<wchar_t>(id.value()) == str);
  ```

* Creating a UUID from a sequence of 16 bytes

  ```cpp
  std::array<uuids::uuid::value_type, 16> arr{{
     0x47, 0x18, 0x38, 0x23,
     0x25, 0x74,
     0x4b, 0xfd,
     0xb4, 0x11,
     0x99, 0xed, 0x17, 0x7d, 0x3e, 0x43}};
  uuid id(arr);

  assert(uuids::to_string(id) == "47183823-2574-4bfd-b411-99ed177d3e43");

  // or

  uuids::uuid::value_type arr[16] = {
     0x47, 0x18, 0x38, 0x23,
     0x25, 0x74,
     0x4b, 0xfd,
     0xb4, 0x11,
     0x99, 0xed, 0x17, 0x7d, 0x3e, 0x43 };
  uuid id(std::begin(arr), std::end(arr));
  assert(uuids::to_string(id) == "47183823-2574-4bfd-b411-99ed177d3e43");
  
  // or 
  
  uuids::uuid id{{
     0x47, 0x18, 0x38, 0x23,
     0x25, 0x74,
     0x4b, 0xfd,
     0xb4, 0x11,
     0x99, 0xed, 0x17, 0x7d, 0x3e, 0x43}};

  assert(uuids::to_string(id) == "47183823-2574-4bfd-b411-99ed177d3e43");
  ```
  
* Comparing UUIDs

  ```cpp
  uuid empty;
  uuid id = uuids::uuid_system_generator{}();
  assert(empty == empty);
  assert(id == id);
  assert(empty != id);
  ```

* Swapping UUIDs

  ```cpp
  uuid empty;
  uuid id = uuids::uuid_system_generator{}();

  assert(empty.is_nil());
  assert(!id.is_nil());

  std::swap(empty, id);

  assert(!empty.is_nil());
  assert(id.is_nil());

  empty.swap(id);

  assert(empty.is_nil());
  assert(!id.is_nil());
  ```
  
* Converting to string

  ```cpp
  uuid empty;
  assert(uuids::to_string(empty) == "00000000-0000-0000-0000-000000000000");
  assert(uuids::to_string<wchar_t>(empty) == L"00000000-0000-0000-0000-000000000000");
  ```

* Using with an orderered associative container

  ```cpp
  std::random_device rd;
  auto seed_data = std::array<int, std::mt19937::state_size> {};
  std::generate(std::begin(seed_data), std::end(seed_data), std::ref(rd));
  std::seed_seq seq(std::begin(seed_data), std::end(seed_data));
  std::mt19937 engine(seq);
  uuids::uuid_random_generator gen(&engine);
   
  std::set<uuids::uuid> ids{uuid{}, gen(), gen(), gen(), gen()};

  assert(ids.size() == 5);
  assert(ids.find(uuid{}) != ids.end());
  ```

* Using in an unordered associative container

  ```cpp
  std::random_device rd;
  auto seed_data = std::array<int, std::mt19937::state_size> {};
  std::generate(std::begin(seed_data), std::end(seed_data), std::ref(rd));
  std::seed_seq seq(std::begin(seed_data), std::end(seed_data));
  std::mt19937 engine(seq);
  uuids::uuid_random_generator gen(&engine);

  std::unordered_set<uuids::uuid> ids{uuid{}, gen(), gen(), gen(), gen()};

  assert(ids.size() == 5);
  assert(ids.find(uuid{}) != ids.end());
  ```

* Hashing UUIDs

  ```cpp
  using namespace std::string_literals;
  auto str = "47183823-2574-4bfd-b411-99ed177d3e43"s;
  uuid id = uuids::uuid::from_string(str).value();

  auto h1 = std::hash<std::string>{};
  auto h2 = std::hash<uuid>{};
  assert(h1(str) == h2(id));
  ```

## Support
The library is supported on all major operating systems: Windows, Linux and Mac OS.

## Dependencies
Because no major compiler supports `std::span` yet the [Microsoft Guidelines Support Library](https://github.com/Microsoft/GSL) (aka GSL) is used for its span implementation (from which the standard version was defined). 

## Testing
A testing project is available in the sources. To build and execute the tests do the following:
* Clone or download this repository
* Create a `build` directory in the root directory of the sources
* Run the command `cmake ..` from the `build` directory; if you do not have CMake you must install it first.
* Build the project created in the previous step
* Run the executable.

## Credits
The SHA1 implementation is based on the [TinySHA1](https://github.com/mohaps/TinySHA1) library.