189 lines
6.2 KiB
Markdown
189 lines
6.2 KiB
Markdown
# stduuid
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A C++ 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:
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* [Universally unique identifier](https://en.wikipedia.org/wiki/Universally_unique_identifier)
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* [A Universally Unique IDentifier (UUID) URN Namespace](https://www.ietf.org/rfc/rfc4122.txt)
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## Library overview
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The library defines a namespace `uuids` with the following types and functions:
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Basic types:
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| Name | Description |
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| ---- | ----------- |
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| `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 string. |
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| `uuid_variant` | a strongly type enum representing the type of a UUID |
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| `uuid_version` | a strongly type enum representing the version of a UUID |
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Generators:
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| Name | Description |
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| ---- | ----------- |
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| `uuid_default_generator` | a function object that generates new UUIDs, using an operating system method to create one (`CoCreateGuid` on Windows, `uuid_generate` on Linux, `CFUUIDCreate` on Mac) |
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| ` basic_uuid_random_generator` | a function object that generates version 4 UUIDs using a pseudo-random number generator engine. |
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| `uuid_random_generator` | a basic_uuid_random_generator using the Marsenne Twister engine, i.e. `basic_uuid_random_generator<std::mt19937>` |
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Utilities:
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| Name | Description |
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| ---- | ----------- |
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| `std::swap<>` | specialization of `swap` for `uuid` |
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| `std::hash<>` | specialization of `hash` for `uuid` (necessary for storing UUIDs in unordered associative containers, such as `std::unordered_set`) |
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Other:
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| Name | Description |
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| ---- | ----------- |
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| `operator==` and `operator!=` | for UUIDs comparison for equality/inequality |
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| `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. |
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| `operator<<` | to write a UUID to an output stream using the canonical textual representation. |
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| `to_string()` | creates a `std::string` with the canonical textual representation of a UUID. |
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| `to_wstring()` | creates a `std::wstring` with the canonical textual representation of a UUID. |
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This project is currently under development and should be ignored until further notice.
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## Using the library
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The following is a list of examples for using the library:
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* Creating a nil UUID
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```
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uuid empty;
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assert(empty.nil());
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assert(empty.size() == 16);
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```
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* Creating a new UUID
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```
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uuid const guid = uuids::uuid_default_generator{}();
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assert(!guid.nil());
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assert(guid.size() == 16);
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assert(guid.version() == uuids::uuid_version::random_number_based);
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assert(guid.variant() == uuids::uuid_variant::rfc);
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```
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* Create a UUID from a string
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```
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using namespace std::string_literals;
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auto str = "47183823-2574-4bfd-b411-99ed177d3e43"s;
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uuid guid(str);
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assert(guid.string() == str);
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```
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or
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```
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auto str = L"47183823-2574-4bfd-b411-99ed177d3e43"s;
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uuid guid(str);
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assert(guid.wstring() == str);
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```
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* Creating a UUID from an array
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```
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std::array<uuids::uuid::value_type, 16> arr{{
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0x47, 0x18, 0x38, 0x23,
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0x25, 0x74,
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0x4b, 0xfd,
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0xb4, 0x11,
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0x99, 0xed, 0x17, 0x7d, 0x3e, 0x43}};
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uuid guid(std::begin(arr), std::end(arr));
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assert(id.string() == "47183823-2574-4bfd-b411-99ed177d3e43");
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```
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or
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```
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uuids::uuid::value_type arr[16] = {
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0x47, 0x18, 0x38, 0x23,
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0x25, 0x74,
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0x4b, 0xfd,
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0xb4, 0x11,
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0x99, 0xed, 0x17, 0x7d, 0x3e, 0x43 };
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uuid guid(std::begin(arr), std::end(arr));
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assert(guid.string() == "47183823-2574-4bfd-b411-99ed177d3e43");
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```
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* Comparing UUIDS
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```
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uuid empty;
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uuid guid = uuids::uuid_default_generator{}();
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assert(empty == empty);
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assert(guid == guid);
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assert(empty != guid);
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```
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* Swapping UUIDS
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```
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uuid empty;
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uuid guid = uuids::uuid_default_generator{}();
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assert(empty.nil());
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assert(!guid.nil());
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std::swap(empty, guid);
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assert(!empty.nil());
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assert(guid.nil());
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empty.swap(guid);
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assert(empty.nil());
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assert(!guid.nil());
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```
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* Converting to string
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```
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uuid empty;
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assert(uuids::to_string(empty) == "00000000-0000-0000-0000-000000000000");
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assert(uuids::to_wstring(empty) == L"00000000-0000-0000-0000-000000000000");
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```
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* Iterating through the UUID data
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```
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std::array<uuids::uuid::value_type, 16> arr{{
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0x47, 0x18, 0x38, 0x23,
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0x25, 0x74,
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0x4b, 0xfd,
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0xb4, 0x11,
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0x99, 0xed, 0x17, 0x7d, 0x3e, 0x43}};
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uuid guid;
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assert(guid.nil());
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std::copy(std::cbegin(arr), std::cend(arr), std::begin(guid));
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assert(!guid.nil());
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assert(guid.string() == "47183823-2574-4bfd-b411-99ed177d3e43");
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size_t i = 0;
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for (auto const & b : guid)
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assert(arr[i++] == b);
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```
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* Using with an orderered associative container
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```
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uuids::uuid_default_generator gen;
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std::set<uuids::uuid> ids{uuid{}, gen(), gen(), gen(), gen()};
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assert(ids.size() == 5);
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assert(ids.find(uuid{}) != ids.end());
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```
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* Using in an unordered associative container
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```
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uuids::uuid_default_generator gen;
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std::unordered_set<uuids::uuid> ids{uuid{}, gen(), gen(), gen(), gen()};
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assert(ids.size() == 5);
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assert(ids.find(uuid{}) != ids.end());
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```
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* Hashing UUIDs
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```
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auto h1 = std::hash<std::string>{};
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auto h2 = std::hash<uuid>{};
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assert(h1(str) == h2(guid));
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```
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## Limitations
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The library can only create new uuids using the underlaying operating system resources.
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An alternative to this library could be the [boost::uuid](http://www.boost.org/doc/libs/1_65_1/libs/uuid/) library. This has a similar model, but supports creating all variant of uuids, including md5 and sha1 name based, time based, and random number based values.
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## Support
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The library is supported on all major operating systems: Windows, Linux and Mac OS.
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## Testing
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A testing project is available in the sources. To build and execute the tests do the following:
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* Clone or download this repository
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* Create a `build` directory in the root directory of the sources
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* Run the command `cmake ..` from the `build` directory; if you do not have CMake you must install it first.
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* Build the project created in the previous step
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* Run the executable.
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