If you look at the values involved (in pairs) of hex digits you can see that the last 7 bytes are the same in both cases, but the first 9 are switched around a bit. Going from your example, but rewriting each pair in the .NET as 00, 11, 22 etc and switching the relevant … Read more
This is an old question, but I had to solve it in order for a system I was working on to be backward compatible. The exact requirement was for a client-generated identifier that would be written to the database and stored in a 20-character unique column. It never got shown to the user and was … Read more
Since Windows 2000 Microsoft uses a version 4 algorithm: With Windows 2000, Microsoft switched to version 4 GUIDs, since embedding the MAC address was viewed as a security risk. 1 You can see that as well from a GUID generated in .NET (from Wikipedia): Version 4 UUIDs have the form xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx with any hexadecimal digits … Read more
Just cast it as a BINARY(16). SELECT category, MIN(CAST(guid AS BINARY(16))) FROM myTable GROUP BY category You can cast it back later if necessary. WITH CategoryValue AS ( SELECT category, MIN(CAST(guid AS BINARY(16))) FROM myTable GROUP BY category ) SELECT category, CAST(guid AS UNIQUEIDENTIFIER) FROM CategoryValue
There’s a really good article on Raymond Chen’s blog that describes how GUIDs are generated, and in particular why a substring of a guid is not guaranteed to be unique. Basically, a a GUID is generated using a combination of: The MAC address of the machine used to generate the GUID (so GUIDs generated on … Read more
The chances of getting two identical guids are astronomically slim even if you are generating guids as fast as you can. (Generating, say, thousands of guids per second for the sole purpose of finding a duplicate.) Of course, if you want my opinion, I do believe that there will be a time, in a couple … Read more
Use the StringFromCLSID function to convert it to a string e.g.: GUID guid; CoCreateGuid(&guid); OLECHAR* guidString; StringFromCLSID(guid, &guidString); // use guidString… // ensure memory is freed ::CoTaskMemFree(guidString); Also see the MSDN definition of a GUID for a description of data4, which is an array containing the last 8 bytes of the GUID
Mark is correct. Value types that define their own equality operators automatically get lifted-to-nullable versions defined as well, for free. The nullable equality operator that takes two nullable guids is applicable in this situation, will be called, and will always return false. In C# 2, this produced a warning, but for some reason, this stopped … Read more
There is no Guid.TryParse in CLR 2.0 and earlier. It will be available starting with CLR 4.0 and Visual Studio 2010. As to why there wasn’t. These types of questions are usually hard to answer correctly. Most likely it was an oversight or a time constraint issue. If you open up mscorlib in reflector you’ll … Read more
In Ubuntu, you can do apt-cache search libuuid to see the available packages relating to the text libuuid. Here’s my output from Ubuntu 9.04: $ apt-cache search libuuid libuuid-perl – Perl extension for using UUID interfaces as defined in e2fsprogs libuuid1 – universally unique id library libuuid1-dbg – Debugging information for libuuid1 uuid-dev – universally … Read more