CrossGuid

CrossGuid is a minimal, cross platform, C++ GUID library. It uses the best native GUID/UUID generator on the given platform and had a generic class for parsing, stringifying, and comparing IDs. The intention is that anyone who uses this code can simply copy guid.h and guid.cpp into their project and define one of the following preprocessor flags to control the implementation:

• GUID_LIBUUID - Uses libuuid which is normally used on linux but possibly usable elsewhere as well.
• GUID_CFUUID - Uses CFCreateUUID from Apple's CoreFoundation framework. This works on both Mac OSX and iOS.
• GUID_WINDOWS - Uses the built in CoCreateGuid function in Windows.
• GUID_ANDROID - Uses JNI to invoke Java functions from Android SDK.

I recommend taking the time to actually look at the guid.h and guid.cpp so that you can see how simple they are. It should be pretty trivial to modify the code to match your naming conventions or drop it into a namespace so that it fits in nicely with your code base.

Basic usage

Tests

The tests are a simple way to figure out how the library works. There is a file in the root of the repository called test.cpp that runs a simple set of tests and outputs a few guid strings for a sanity check. This file does not have a main() function entry point there, it is intended to be called from somewhere else, and it takes a GuidGenerator as input. All platforms except for Android use testmain.cpp to construct a GuidGenerator and run the tests. In Android there is a special file called android/jni/jnitest.cpp which invokes the tests.

Creating a guid generator

Creation of a guid generator is not exactly the same in every platform, but this is an intentional feature. In Android the guid generation function has to have access to a JNIEnv handle, but that handle is not necessarily the same all the time. Therefore, there is a GuidGenerator class whose construction is different depending on the platform, but client code can pass around a GuidGenerator object and then use it the same on every platform. On every platform except Android, you can create a guid generator like this:

GuidGenerator generator;

But on Android you need to pass a JNIEnv *:

GuidGenerator generator(env);

Creating guids

On every platform guid creation is the same:

void doGuidStuff(GuidGenerator generator)
{
    auto myGuid = generator.newGuid();
}

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(GuidGenerator generator)
{
    auto myGuid = generator.newGuid();
    std::cout << "Here is a guid: " << myGuid << std::endl;
}

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

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

Parsing a string into a guid

There is a constructor that can be used to create a guid from a string without needing any reference to a GuidGenerator:

void doGuidStuff()
{
    Guid guid("e63e03a8-f3e5-4e0f-99bb-a3fc402d4fc8");
}

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(const vector<unsigned char> &bytes);

and

Guid(const unsigned char *bytes);

In both cases the constructor expects to receive exactly 16 bytes.

Comparing guids

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

void doGuidStuff(GuidGenerator generator)
{
    auto guid1 = generator.newGuid();
    auto guid2 = generator.newGuid();
    
    auto guidsAreEqual = guid1 == guid2;
    auto guidsAreNotEqual = guid1 != guid2;
}

Linux

The Linux version uses the proprocessor flag GUID_LIBUUID

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

Then you can compile and run tests with:

./linux.sh

Mac/iOS

The Mac and iOS versions use the preprocessor flag GUID_CFUUID

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++. If you have the command line tools that come with Xcode installed, then you can compile and run the tests like this:

./mac.sh

Windows

The Windows version uses the preprocessor flag GUID_WINDOWS

On Windows we just the the built-in function CoCreateGuid. There is a Visual Studio 2013 solution in the VisualStudio directory which you can use to compile and run tests.

Android

The Android version uses the preprocessor flag GUID_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.
• ndk-build and other ndk cross-compile tools are in your path.
• You have a jdk setup including JAVA_HOME environment variable.

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.