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.

For information about UUID/GUIDs see:

• Universally unique identifier
• A Universally Unique IDentifier (UUID) URN Namespace

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:

Generators:

Utilities:

Constants:

Other:

This library is an implementation of the proposal P0959.

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.

The following is a list of examples for using the library:

• Creating a nil UUID

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

• Creating a new UUID

  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

  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);
  uuids::uuid_random_generator gen{generator};
  
  uuid const id = gen();
  assert(!id.is_nil());
  assert(id.as_bytes().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

  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.as_bytes().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

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

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

• Creating a UUID from a sequence of 16 bytes

  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

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

• Swapping UUIDs

  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

  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

  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

  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

  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));

If you generate uuids using the basic_uuid_random_generator and std::random_device to seed a generator, keep in mind that this might not be non-deterministic and actually generate the same sequence of numbers:

std::random_device may be implemented in terms of an implementation-defined pseudo-random number engine if a non-deterministic source (e.g. a hardware device) is not available to the implementation. In this case each std::random_device object may generate the same number sequence.

This could be a problem with MinGW. See Bug 85494 - implementation of random_device on mingw is useless. This was fixed in GCC 9.2.

A portable alternative is to use the Boost.Random library.

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

If you use the library in a project built with C++20, then you can use std::span. This is used by default, if the header is supported by your compiler. The check is done with the __cpp_lib_span feature-test macro.

Otherwise, such as when building with C++17, std::span is not available. However, the Microsoft Guidelines Support Library (aka GSL) can be used for its span implementation (from which the standard version was defined). The stduuid library defaults to use this implementation if std::span is not available.

To ensure gsl::span can be used, make sure the GSL library is available, and the GSL include directory is listed in the include directories for the project.

If you use cmake to build the test project, make sure the variable called UUID_USING_CXX20_SPAN is not defined, or it's value is OFF (this is the default value). This will ensure the gsl directory will be included in the search list of header directories.

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.

Examples

To generate a project files for Visual Studio 2019, you can run the following commands:

cd build
cmake -G "Visual Studio 17" -A x64 ..

To enable the operating system uuid generator set the UUID_SYSTEM_GENERATOR variable to ON.

cd build
cmake -G "Visual Studio 17" -A x64 -DUUID_SYSTEM_GENERATOR=ON ..

To enable the experimental time-based uuid generator set the UUID_TIME_GENERATOR variable to ON.

cd build
cmake -G "Visual Studio 17" -A x64 -DUUID_TIME_GENERATOR=ON ..

The SHA1 implementation is based on the TinySHA1 library.