Re-matching takes a very long time to complete

Question

I wrote a regular expression that parses the file path to another group (DRIVE, DIR, FILE, EXTENSION).

^((?<DRIVE>[a-zA-Z]):\\)*((?<DIR>[a-zA-Z0-9_]+(([a-zA-Z0-9_\s_\-\.]*[a-zA-Z0-9_]+)|([a-zA-Z0-9_]+)))\\)*(?<FILE>([a-zA-Z0-9_]+(([a-zA-Z0-9_\s_\-\.]*[a-zA-Z0-9_]+)|([a-zA-Z0-9_]+))\.(?<EXTENSION>[a-zA-Z0-9]{1,6})$))

I did a test in C #. When the path I want to check is correct. The result is very fast, and this is what I wanted to expect.

string path = @"C:\Documents and Settings\jhr\My Documents\Visual Studio 2010\Projects\FileEncryptor\Dds.FileEncryptor\Dds.FileEncryptor.csproj";

=> OK

But when I try to check a path that I know that will not match, for example:

string path = @"C:\Documents and Settings\jhr\My Documents\Visual Studio 2010\Projects\FileEncryptor\Dds.FileEncryptor\Dds.FileEncryptor?!??????";

=> ERROR

The test freezes when I call this piece of code

Match match = s_fileRegex.Match(path);

When I look at my Process Explorer, I see that the QTAgent32.exe process is hanging on 100% of my processor. What does it mean?

Answer 1

, , , string, - backtracking .NET.

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((?<DRIVE>[a-zA-Z]):\\)*

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Answer 2

, , , , , .

,

(?<FILE>
  ([a-zA-Z0-9_]+
    (
      ([a-zA-Z0-9_\s_\-\.]*[a-zA-Z0-9_]+)
    |
      ([a-zA-Z0-9_]+)
    )\.
    (?<EXTENSION>[a-zA-Z0-9]{1,6})
  $)
)

,

([a-zA-Z0-9_\s_\-\.]*[a-zA-Z0-9_]+)
|
([a-zA-Z0-9_]+)

, .

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Answer 3

System.IO.Path?

• : http://msdn.microsoft.com/en-us/library/system.io.path.getpathroot.aspx

• : http://msdn.microsoft.com/en-us/library/system.io.path.getdirectoryname.aspx ,

• : http://msdn.microsoft.com/en-us/library/system.io.path.getfilenamewithoutextension.aspx

• : http://msdn.microsoft.com/en-us/library/system.io.path.getextension.aspx

Answer 4

FileInfo Path .

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