Question

I want to try to convert a string to a Guid, but I don’t want to rely on catching exceptions (

• for performance reasons – exceptions are expensive
• for usability reasons – the debugger pops up
• for design reasons – the expected is not exceptional

In other words the code:

public static Boolean TryStrToGuid(String s, out Guid value) {     try     {         value = new Guid(s);         return true;     }     catch (FormatException)     {         value = Guid.Empty;         return false;     } } 

is not suitable.

I would try using RegEx, but since the guid can be parenthesis wrapped, brace wrapped, none wrapped, makes it hard.

Additionally, I thought certain Guid values are invalid(?)

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Update 1

ChristianK had a good idea to catch only FormatException, rather than all. Changed the question’s code sample to include suggestion.

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Update 2

Why worry about thrown exceptions? Am I really expecting invalid GUIDs all that often?

The answer is yes. That is why I am using TryStrToGuid – I am expecting bad data.

Example 1 Namespace extensions can be specified by appending a GUID to a folder name. I might be parsing folder names, checking to see if the text after the final . is a GUID.

c:\Program Files c:\Program Files.old c:\Users c:\Users.old c:\UserManager.{CE7F5AA5-6832-43FE-BAE1-80D14CD8F666} c:\Windows c:\Windows.old 

Example 2 I might be running a heavily used web-server wants to check the validity of some posted back data. I don’t want invalid data tying up resources 2-3 orders of magnitude higher than it needs to be.

Example 3 I might be parsing a search expression entered by a user.

If they enter GUID’s I want to process them specially (such as specifically searching for that object, or highlight and format that specific search term in the response text.)

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Update 3 – Performance benchmarks

Test converting 10,000 good Guids, and 10,000 bad Guids.

Catch FormatException:    10,000 good:     63,668 ticks    10,000 bad:   6,435,609 ticks  Regex Pre-Screen with try-catch:    10,000 good:    637,633 ticks    10,000 bad:     717,894 ticks  COM Interop CLSIDFromString    10,000 good:    126,120 ticks    10,000 bad:      23,134 ticks 

p.s. I shouldn’t have to justify a question.

Answer 1

Performance Benchmarks

Catch exception:    10,000 good:    63,668 ticks    10,000 bad:  6,435,609 ticks  Regex Pre-Screen:    10,000 good:   637,633 ticks    10,000 bad:    717,894 ticks  COM Interop CLSIDFromString    10,000 good:   126,120 ticks    10,000 bad:     23,134 ticks 

COM Intertop (Fastest) Answer:

/// <summary> /// Attempts to convert a string to a guid. /// </summary> /// <param name='s'>The string to try to convert</param> /// <param name='value'>Upon return will contain the Guid</param> /// <returns>Returns true if successful, otherwise false</returns> public static Boolean TryStrToGuid(String s, out Guid value) {    //ClsidFromString returns the empty guid for null strings       if ((s == null) || (s == ''))       {             value = Guid.Empty;             return false;       }     int hresult = PInvoke.ObjBase.CLSIDFromString(s, out value);    if (hresult >= 0)    {       return true;    }    else    {       value = Guid.Empty;       return false;    } }   namespace PInvoke {     class ObjBase     {         /// <summary>         /// This function converts a string generated by the StringFromCLSID function back into the original class identifier.         /// </summary>         /// <param name='sz'>String that represents the class identifier</param>         /// <param name='clsid'>On return will contain the class identifier</param>         /// <returns>         /// Positive or zero if class identifier was obtained successfully         /// Negative if the call failed         /// </returns>         [DllImport('ole32.dll', CharSet = CharSet.Unicode, ExactSpelling = true, PreserveSig = true)]         public static extern int CLSIDFromString(string sz, out Guid clsid);     } } 

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Bottom line: If you need to check if a string is a guid, and you care about performance, use COM Interop.

If you need to convert a guid in String representation to a Guid, use

new Guid(someString);