Check if a file/directory exists: is there a better way?

Question

I find myself doing this a lot just to ensure the filename is not in use. Is there a better way?

Directory.Exists(name) || File.Exists(name)

Higgledypiggledy

And what is wrong with that? How can it get any easier or cleaner? – Fiji

I do it everywhere.... its ugly. Usually i dont worry about precedence but it could happen – Higgledypiggledy

Why do you need these 2 checks? Why don't you use just File.Exists(name) ? – Chesnut

@Egor4eg: three years to late but I imagine I was checking if a filename was free to use or not. Although I normally just do File.Create or whatever, I probably was doing it in UI and wanted to stop the user if the file existed before finishing everything in the UI/doing the ops – Higgledypiggledy

The filesystem has a tendency to laugh in your face, and make the file in use after you check it. In the general case, the only way to be sure if a filename is not in use is to try to create it, and if it fails, checking why. It's not completely unreasonable to check if it exists first for fail-fast behaviour, but don't count on it being correct. – Doura

Answer 1

Sure :)

internal static bool FileOrDirectoryExists(string name)
{
   return (Directory.Exists(name) || File.Exists(name));
}

Allocution

Extension method for Path class? "Performs operations on String instances that contain file or directory path information." – Boliviano

Si. semi good idea for having it in a string instance. its really to bad .NET doesnt allow extending a static class :( – Higgledypiggledy

anyone notice ;expected error ?.xD 2014ppl from here, but still thanks @Allocution . – Ergot

@si618, you cannot create extension methods for static classes. Can you? – Sunbathe

True, acidzombie and Jordan are correct, you need an instance to write an extension method. – Boliviano

HInt: To save time put the most common check first in the or expression. If the first part returns true the second part of the expression will not be evaluated. – Funch

OP is probably looking for something like Python's os.path.exists rather. Also see Leon's answer below: https://mcmap.net/q/138828/-check-if-a-file-directory-exists-is-there-a-better-way – Cliffcliffes

Answer 2

Note that the fact that you are using Exists() to check for file or directory name in use is subject to race conditions.

At any point after your Exists() test has passed, something could have created a file with that name before your code reaches the point where you create a file, for example.

(I'm assuming it is an exceptional condition for the file to already exist).

It is more reliable to simply to open the file, specifying an appropriate FileShare parameter.

Example:

using System;
using System.IO;

static class FileNameInUse
{
    static void Main(string[] args)
    {
        string path = args[0];
        using (var stream = File.Open(path, FileMode.CreateNew, FileAccess.Write, FileShare.None))
        {
            // Write to file
        }
    }
}

So simply handling the IOException on failure may result in simpler code less prone to race conditions, because now:

• If something else has already created the file, FileMode.CreateNew will cause an IOException to be thrown
• If your open and create succeeds, because of FileShare.None, no other process can access the file until you close it.

Unfortunately, it is not possible to check whether a file is currently in use, and not throw an exception, without some ugly P/Invoke:

    bool IsFileInUse(string fileName)
    {
            IntPtr hFile = Win32.CreateFile(fileName, Win32.FILE_READ_DATA, 0, IntPtr.Zero, Win32.OPEN_EXISTING, Win32.FILE_ATTRIBUTE_NORMAL, IntPtr.Zero);
            if (hFile.ToInt32() == Win32.INVALID_HANDLE_VALUE)
                return true;

            Win32.CloseHandle(hFile);
            return false;
    }

    class Win32
    {
        const uint FILE_READ_DATA = 0x0001;
        const uint FILE_SHARE_NONE = 0x00000000;
        const uint FILE_ATTRIBUTE_NORMAL = 0x00000080;
        const uint OPEN_EXISTING = 3;
        const int INVALID_HANDLE_VALUE = -1;

        [DllImport("kernel32.dll", SetLastError=true)]
        internal static extern IntPtr CreateFile(string lpFileName,
                                               uint dwDesiredAccess,
                                               uint dwShareMode,
                                               IntPtr lpSecurityAttributes,
                                               uint dwCreationDisposition,
                                               uint dwFlagsAndAttributes,
                                               IntPtr hTemplateFile);

        [DllImport("kernel32.dll")]
        internal static extern bool CloseHandle(IntPtr hObject);
    }

And this fast check is also prone to race conditions, unless you return the file handle from it, and pass that to the relevant FileStream constructor.

Gully

For some reason people never seem to get recognized for solving the problem, only for answering the question. +1 for answering the question that SHOULD have been asked. – Locket

+1. @Ben Voigt: Well theres no way for anyone to know the problem since i specified it BUT my question is WHAT I WANTED TO KNOW. I am actually using .Exist to check if my app created a temp folder (which it searches for a nonexisting folder and creates one then passing the name). I could just do a try{Directory.Delete()}catch but i prefer exist for convince. Under no circumstance should anything other then my app delete the folder. The folder is renamed once succeeded. So Leon actually didnt solve my problem. – Higgledypiggledy

@Ben Voigt: actually i was wrong. In that case i use Directory.delete but when i create the directory i use that line to check if it exist then i use either Directory.CreateDirectory or file.open with the return filename. I use the function to generate the unique name in a specific format. – Higgledypiggledy

@Ben: Thanks for the kind words, but I was just taking a guess. I've been bitten in the past by this type of thing, and thought I recognized a potential problem :) – Gully

+1 @Leon - For "At any point after your Exists() test has passed, something could have created a file with that name before your code reaches the point where you create a file, for example.." – Simonson

Answer 3

I think that's the only way. I generally have a "FileManager" class which have static methods encapsulating I/O methods including the ones you indicated and then use that "FileManager" across all the applications as a library.

Simonson

Answer 4

My way of checking this is using the FileSystemInfo, here is my code:

FileSystemInfo info = 
  File.GetAttributes(data.Path).HasFlag(FileAttributes.Directory) ? 
    new DirectoryInfo(data.Path) : (FileSystemInfo)new FileInfo(data.Path);

return info.Exists;

Splashy

File.GetAttributes throws a System.IO.FileNotFoundException if neither a file nor directory exists – Liman

Yep, does not work with FileSystemWatcher, because the path could be a deleted file – Chagall

Answer 5

You can use following function:

[DllImport("shlwapi", EntryPoint = "PathFileExists", CharSet = CharSet.Unicode)]
public static extern bool PathExists(string path);

Bushwa

It is useful when need to check presence of FS entry while working with P/Invoke, thanks! – Topmost

Answer 6

The following line works (.NET8), but the accepted solution might have better performance (if that matters here)

var pathExists = new FileInfo(path).Attributes > 0;

Mathildamathilde

Answer 7

Another way to check if file exist.

FileInfo file = new FileInfo("file.txt");

if (file.Exists)
{
    // TO DO
}

Peashooter

Look at the tags before you post an answer. – Globetrotter

Tag is C# , .NET and file. This is C# code and it can yield desired output. – Peashooter

+1 to even this out. weird that anyone would downvote :|. actually, not to even out. i would upvote this anyways. interesting and good answer. – Higgledypiggledy

The down vote is a necessity as this is a wrong answer. A fileinfo Exists call returns false on all directories even if they exist. From the FileInfo.Exists page: true if the file exists; false if the file does not exist or if the file is a directory – Keithakeithley

Instead file name "file.txt" must be file path: msdn.microsoft.com/en-us/library/… – Scarabaeid

Answer 8

How about checking whether FileAttributes == -1?

public static bool PathExists(this string path) {
    DirectoryInfo dirInfo = null;
    try { dirInfo = new DirectoryInfo(path.TrimEnd(Path.DirectorySeparatorChar)); }
    catch { }
    if (dirInfo == null || dirInfo.Attributes == (FileAttributes)(-1))
        return false;
    return true;
}

Jeseniajesh

Answer 9

Check if a directory Exists

string root = @"C:\Temp";        
// If directory does not exist, don't even try   
if (Directory.Exists(root))  
{  
    Directory.Delete(root);  
}  

Use the File.exists method in C# to check if a file exits in C# or not. Firstly, check whether the file is present in the current directory.

if (File.Exists("MyFile.txt")) {
   Console.WriteLine("The file exists.");
}

After that check whether the file exist in a directory or not

if (File.Exists(@"D:\myfile.txt")) {
   Console.WriteLine("The file exists.");
}

Lianaliane

Answer 10

bool FileOrDirectoryExists(string path)
{
    try
    {
        File.GetAttributes(_source);
    }
    catch (FileNotFoundException)
    {
        return false;
    }
    return true;
}

Rightist

The point of testing to see if a path and file exist is typically to avoid an exception. If you're going to rely on the error handler, why not just omit the checks completely? – Merola