Why are there dashes in a .NET GUID?

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Why are there dashes in a .NET GUID? Are there dashes in most implementations of a GUID, or is it just a Microsoft thing?



Technically, there are no "dashes" in a GUID. A GUID is a 128-bit value which is usually stored in the following manner (using C# here to represent the structure):

public struct Guid
  public ulong Data1;
  public ushort Data2;
  public ushort Data3;
  public fixed byte Data4[8];

The dashes are in the string representation of a GUID.

The dashes are optional and are not required in a string representation of a GUID.

That said, there are historical reasons as to where the placement of the dashes are, related to how the GUIDs were generated, but that historical semantic no longer applies.

Any reason behind hyphens in a GUID?, The hyphens are always placed at the same position, so you won't lose any information (or unique-ness) by removing NET GUID? for a detailed explanation. Just when I generated a GUID, I found some hyphens in between the character and also at specified intervals. 8b55fec7-c987-4e7b-abad-16e5aaea9b53 Is there any story behind this? Note: My intention is to remove those hyphens as I am adding this GUID to a filename and our filename should only be aplhanumeric.

In the initial version of the UUID (Universally Unique Identifier) specification, each of the data elements had a semantic meaning:

{ time_low } – { time_mid } – { time_high_and_version } – { clock_seq_and_reserved clock_seq_low } – { node_id }

These elements were designed to provide temporal (time bits), and spatial (host bits) uniqueness.

Version History

As the the mathematical probability of collisions in a keyspace of 2^1024 random bits was found to be astronomically improbable, subsequent versions of the UUID spec have phased out the time and host data for security and privacy reasons.

The only elements that retain any meaning are the version bits and the reserved bits.

Version 3 UUIDs are derived from an MD5 hash of a URI or other Distinguished Name.

Version 4 is generated with random data and is, currently, the most common implementation you'll see in the wild.

Version 5 is derived from a SHA1 hash.

Storage formats

Since the hyphens are specified for the ASCII formatting of UUIDs in the RFC, even though the individual sections no longer retain their original meaning, they are still required if you need interoperability.

UUIDs are also sometimes stored as a base64 or ascii85 encoded string to save space for transmission over transports that are not binary-safe, and adherence to the RFC is not required.

Ascii:   3F2504E0-4F89-11D3-9A0C-0305E82C3301
Base64:  7QDBkvCA1+B9K/U0vrQx1A
Ascii85: 5:$Hj:Pf\4RLB9%kU\Lj

References: RFC4122 (see page 3 specifically for the ABNF description of the UUID format) Wikipedia GUID UUID

Guid.TryParseExact Method (System), Converts span of characters representing the GUID to the equivalent structure, provided that the NET .NET API browser � System � Guid � Methods; TryParseExact Converts the string representation of a GUID to the equivalent Guid structure, provided that the P, 32 digits separated by hyphens, enclosed in parentheses: I've got a file with 200 or so GUID's scattered throughout that have had their dashes removed. I need to put these dashes back in but doing it manually would be tedious and time consuming. Is there a way to do a replace all, perhaps in notepad++, to place dashes in the GUIDS?

Hyphens denote the byte structure of a Guid.

typedef struct _GUID 
   DWORD Data1;  
   WORD Data2;  
   WORD Data3;  
   BYTE Data4[8];



You can probably strip them before saving. At least in .NET the constructor of the Guid type will initialize a Guid variable from its string representation regardless of whether the hyphens are still there or removed.

What is the string length of a GUID?, NET (Guid.NewGuid) - class System.Guid. What is the length of the varchar I should expect from a Note: 36 is the string length with the dashes in between. As Adam Davis stated, the Microsoft style is HEX encoding (with braces and dashes to make it more readable) that can be displayed using a subset of ASCII characters (0-9 and A-F), but this is not specifically ASCII encoding.

You can get your guid in various formats.

Assuming you're using c#:

Guid guid = Guid.NewGuid();









Free Online GUID Generator, How many GUIDs do you want (1-2000): Uppcase: {} Braces: Hyphens: at your own risk! No guarantee of their uniqueness or suitability is given or implied. The value of this Guid, formatted by using the "D" format specifier as follows: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx. where the value of the GUID is represented as a series of lowercase hexadecimal digits in groups of 8, 4, 4, 4, and 12 digits and separated by hyphens. An example of a return value is "382c74c3-721d-4f34-80e5-57657b6cbc27".

It's just a convenience.


GUID Converter, GUIDs are represented in Oracle using a RAW(16) datatype. Unfortunately, the byte order is different from the standard hyphen-separated GUIDs used in other� Why are there dashes in a .NET GUID? 48. String replaceAll() vs. Matcher replaceAll() (Performance differences) 8. ORACLE RAW in string format to Standard GUID. 2.

[SOLVED], I suggest to change the code to the following: public List<Data.Country> GetCountryData(string filePath) { string csvRead = File. To test, I made huge and quasi-random trees, using ToString("N") on Guid to get texts I could search for. The control displays how many matches there are, highlights the matching nodes, scrolls the first match into view, and lets the user navigate next/prev match (w/wrap-around).

"GUID should contain 32 digits with 4 dashes" error when , Install the latest June version of SQLOPS, execute it and enter a known server with known Windows Authentication (which we currently use for� By default letters are lowercase. A Guid with only uppercase letters can only be achieved by manually converting them all to uppercase, example: Guid.NewGuid().ToString("N").ToUpper(); A guid with only either letter or digits makes no sense. A guid string representation is hexadecimal, and thus will always (well most likely) contain both.

How to create a GUID in C#.Net, Replace the above line with the below line. Guid guid = Guid.NewGuid();. generate GUID without hyphen. The Oracle Database SYS_GUID function does not return a standard GUID, despite the name. Instead, it returns a 16-byte 128-bit RAW value based on a host identifier and a process or thread identifier, somewhat similar to a GUID. PostgreSQL contains a UUID datatype and can generate most versions of UUIDs through the use of functions from modules.

  • Interesting question. I must say that I've never stopped to think about it.
  • GUIDs have the same amount of entropy regardless of whether they have hyphens in them.
  • The hyphens are only used when displaying one as text. The real UUID is a binary string/array of 16 bytes.
  • This is just totally and completely incorrect, there are 5 hyphenated elements in hyphenated ASCII Hex representation of a GUID, the struct that contains the elements of binary GUID is only 4 elements long. Also, the historical semantics definitely do still apply, especially in this question, considering that history is the exact reason why the hyphens are there in the first place.
  • @joshperry You've reiterated my point from the answer. A Guid is just 128 bytes, period. The separators are from the representation. Also, in regards to the historical semantics applying in the representation, they don't. As you said, it's for historical reasons. Those historical reasons don't apply anymore. From your answer, "these data elements no longer have any specific meaning."
  • I'm not sure where I reiterated that a GUID is 128 bytes, but your second paragraph (about the hyphens having correspondence to the struct) is patently inaccurate. The hyphens are there because that layout is specified in the UUID RFC and has nothing to do with that structure. It is true that the segments in contemporary UUIDs do not necessarily mean what they used to, however, they are there because of what they used to mean. So I guess they are now there because the RFC says so and if you want/need to create interoperable URNs then you'll follow the RFC.
  • @joshperry Removed the part about the placement of the dashes, and left how they are optional. That should satisfy your point.
  • Well, that's true, but you can't use parts of that struct in any meaningful way, can you?
  • But why the extra hyphen within Data4?
  • Look here for an explanation: en.wikipedia.org/wiki/Globally_unique_identifier
  • Correction, a Guid is not a class, it's a value type.