CrossGuid

CrossGuid is a minimal, cross platform, C++ GUID library. It uses the best native GUID/UUID generator on the given platform and has a generic class for parsing, stringifying, and comparing IDs. The guid generation technique is determined by your platform:

Linux

On linux you can use libuuid which is pretty standard. On distros like Ubuntu it is available by default but to use it you need the header files so you have to do:

sudo apt-get install uuid-dev

Mac/iOS

On Mac or iOS you can use CFUUIDCreate from CoreFoundation. Since it's a plain C function you don't even need to compile as Objective-C++.

Windows

On Windows we just use the the built-in function CoCreateGuid. CMake can generate a Visual Studio project if that's your thing.

Android

The Android version uses a handle to a JNIEnv object to invoke the randomUUID() function on java.util.UUID from C++. The Android specific code is all in the android/ subdirectory. If you have an emulator already running, then you can run the android.sh script in the root directory. It has the following requirements:

• Android emulator is already running (or you have physical device connected).
• You're using bash.
• adb is in your path.
• You have an Android sdk setup including ANDROID_HOME environment variable.

Versions

This is version 0.2 of CrossGuid. If you all already using CrossGuid and your code uses GuidGenerator then you are using version 0.1. Differences in version 0.2:

• Put everything inside the namespace xg instead of using the global namespace.
• Removed GuidGenerator class and replaced with the free function xg::newGuid. This is the way I originally wanted it to work but since Android is a special snowflake requiring state (JNIEnv *) I introduced the GuidGenerator class specifically so that there would be somewhere to store the JNIEnv * when running on Android. However, this basically meant complicating the library for the sake of one platform. In version 0.2 the goal is to design for the normal platforms and let Android be weird. In Android you just need to run xg::initJni(JNIEnv *) before you create any guids. The JNIEnv * is just stored as a global variable.
• Added CMake build system. Instead of different scripts for each platform you can just run cmake and it should handle each platform (except Android which again is special).
• Actual guid bytes are stored in std::array<unsigned char, 16> instead of std::vector<unsigned char>.
• More error checking (like if you try to create a guid with invalid number of bytes).

If you're happily using version 0.1 then there's not really any reason to change.

Compiling

Just do the normal cmake thing:

mkdir build
cd build
cmake ..
make install

Running tests

After compiling as described above you should get two files: libcrossguid.a (the static library) and crossguid-test (the test runner). So to run the tests just do:

./crossguid-test

Basic usage

Creating guids

Create a new random guid:

#include <crossguid/guid.hpp>
...
auto g = xg::newGuid();

NOTE: On Android you need to call xg::initJni(JNIEnv *) first so that it is possible for xg::newGuid() to call back into java libraries. initJni only needs to be called once when the process starts.

Create a new zero guid:

xg::Guid g;

Create from a string:

xg::Guid g("c405c66c-ccbb-4ffd-9b62-c286c0fd7a3b");

Checking validity

If you have some string value and you need to check whether it is a valid guid then you can simply attempt to construct the guid:

xg::Guid g("bad-guid-string");
if (!g.isValid())
{
	// do stuff
}

If the guid string is not valid then all bytes are set to zero and isValid() returns false.

Converting guid to string

First of all, there is normally no reason to convert a guid to a string except for in debugging or when serializing for API calls or whatever. You should definitely avoid storing guids as strings or using strings for any computations. If you do need to convert a guid to a string, then you can utilize strings because the << operator is overloaded. To print a guid to std::cout:

void doGuidStuff()
{
    auto myGuid = xg::newGuid();
    std::cout << "Here is a guid: " << myGuid << std::endl;
}

Or to store a guid in a std::string:

void doGuidStuff()
{
    auto myGuid = xg::newGuid();
    std::stringstream stream;
    stream << myGuid;
    auto guidString = stream.str();
}

There is also a str() function that returns a std::string:

std::string guidStr = xg::newGuid().str();

Creating a guid from raw bytes

It's unlikely that you will need this, but this is done within the library internally to construct a Guid object from the raw data given by the system's built-in guid generation function. There are two key constructors for this:

Guid(std::array<unsigned char, 16> &bytes);

and

Guid(const unsigned char * bytes);

When possible prefer the std::array constructor because it is safer. If you pass in an incorrectly sized C array then bad things will happen.

Comparing guids

== and != are implemented, so the following works as expected:

void doGuidStuff()
{
    auto guid1 = xg::newGuid();
    auto guid2 = xg::newGuid();

    auto guidsAreEqual = guid1 == guid2;
    auto guidsAreNotEqual = guid1 != guid2;
}

Hashing guids

Guids can be used directly in containers requireing std::hash such as std::map,std::unordered_map` etc.

License

The MIT License (MIT)

Copyright (c) 2014 Graeme Hill (http://graemehill.ca)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.