README.md

File.Exists alternatives benchmarks

Is it File.Exists slow or not? There are some answers:

• https://stackoverflow.com/questions/2225415/why-is-file-exists-much-slower-when-the-file-does-not-exist
• https://stackoverflow.com/questions/1707569/is-file-exists-an-expensive-operation

Possible implementations:

1. Traditional uses File.Exists

public bool File_Exists(string fileName) =>  File.Exists(fileName);

2. Using P/Invoke PathFileExists

[System.Runtime.InteropServices.DllImport("shlwapi.dll", EntryPoint = "PathFileExistsW", SetLastError = true, CharSet = CharSet.Unicode)]
[return: MarshalAs(UnmanagedType.Bool)]
private static extern bool _PathFileExists([MarshalAs(UnmanagedType.LPWStr)]string pszPath);

public bool PathFileExists(string fileName) => _PathFileExists(fileName);

3. Using FileInfo class

public bool FileInfo(string fileName) => (new FileInfo(fileName)).Exists;

4. Using FileInfo class with try ... catch block

public bool FileInfo_TryCatch(string fileName)
{
    try
    {
        return (new FileInfo(fileName)).Exists;
    }
    catch (Exception)
    {
        return false;
    }
}

Parameters should cover possible cases

@"C:\TEMP\test.txt", // File exists
@"C:\TEMP\test.not", // File not exist
@"\\10.187.39.110\Temp\test.txt", // File exists
@"\\10.187.39.110\Temp\test.not", // File not exists
@"Z:\test.txt", // File exists, map Z: \\10.187.39.110\Temp
@"Z:\test.not", // File not exists, map Z: \\10.187.39.110\Temp
@"J:\test.not", // File not exists, network drive is inactive

Temporary folder on system drive C: (SSD drive) and network file with UNC or mapped drive letter. Connection to network file uses VPN.

Using BenchmarkDotNet

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.18363.657 (1909/November2018Update/19H2)
Intel Core i5-7200U CPU 2.50GHz (Kaby Lake), 1 CPU, 4 logical and 2 physical cores
  [Host]     : .NET Framework 4.8 (4.8.4121.0), X86 LegacyJIT
  DefaultJob : .NET Framework 4.8 (4.8.4121.0), X86 LegacyJIT

First run with connected VPN.

Method	fileName	Mean	Error	StdDev	Median	Ratio	RatioSD
File_Exists	C:\TEMP\test.not	29.88 μs	0.401 μs	0.335 μs	29.83 μs	1.00	0.00
PathFileExists	C:\TEMP\test.not	31.81 μs	0.619 μs	0.867 μs	31.53 μs	1.07	0.03
FileInfo	C:\TEMP\test.not	30.05 μs	0.572 μs	0.507 μs	29.82 μs	1.01	0.02
FileInfo_TryCatch	C:\TEMP\test.not	30.25 μs	0.603 μs	0.645 μs	29.96 μs	1.01	0.03
File_Exists	C:\TEMP\test.txt	46.10 μs	0.602 μs	0.503 μs	45.83 μs	1.00	0.00
PathFileExists	C:\TEMP\test.txt	46.36 μs	0.251 μs	0.196 μs	46.31 μs	1.01	0.01
FileInfo	C:\TEMP\test.txt	46.59 μs	0.422 μs	0.395 μs	46.71 μs	1.01	0.02
FileInfo_TryCatch	C:\TEMP\test.txt	46.33 μs	0.453 μs	0.378 μs	46.24 μs	1.01	0.01
File_Exists	J:\test.not	110.75 μs	1.002 μs	1.113 μs	111.00 μs	1.00	0.00
PathFileExists	J:\test.not	111.92 μs	1.912 μs	2.125 μs	111.14 μs	1.01	0.02
FileInfo	J:\test.not	111.52 μs	1.240 μs	1.523 μs	111.14 μs	1.01	0.02
FileInfo_TryCatch	J:\test.not	111.58 μs	1.826 μs	1.708 μs	110.86 μs	1.01	0.02
File_Exists	Z:\test.not	99.31 μs	1.643 μs	1.283 μs	99.06 μs	1.00	0.00
PathFileExists	Z:\test.not	104.36 μs	2.059 μs	3.607 μs	105.16 μs	1.02	0.04
FileInfo	Z:\test.not	105.06 μs	2.088 μs	5.426 μs	103.23 μs	1.11	0.05
FileInfo_TryCatch	Z:\test.not	101.12 μs	1.630 μs	2.176 μs	100.61 μs	1.03	0.03
File_Exists	Z:\test.txt	185.40 μs	1.456 μs	1.216 μs	185.10 μs	1.00	0.00
PathFileExists	Z:\test.txt	187.29 μs	1.984 μs	1.549 μs	186.99 μs	1.01	0.01
FileInfo	Z:\test.txt	187.18 μs	1.797 μs	1.593 μs	187.37 μs	1.01	0.01
FileInfo_TryCatch	Z:\test.txt	187.08 μs	1.464 μs	1.222 μs	186.99 μs	1.01	0.01
File_Exists	\10.(...)t.not [29]	105.27 μs	1.082 μs	0.904 μs	105.37 μs	1.00	0.00
PathFileExists	\10.(...)t.not [29]	104.61 μs	1.111 μs	0.928 μs	104.34 μs	0.99	0.02
FileInfo	\10.(...)t.not [29]	105.74 μs	0.974 μs	0.863 μs	105.59 μs	1.01	0.01
FileInfo_TryCatch	\10.(...)t.not [29]	105.84 μs	1.374 μs	1.738 μs	105.52 μs	1.01	0.02
File_Exists	\10.(...)t.txt [29]	191.20 μs	1.712 μs	1.430 μs	191.02 μs	1.00	0.00
PathFileExists	\10.(...)t.txt [29]	192.39 μs	2.864 μs	2.539 μs	191.16 μs	1.01	0.02
FileInfo	\10.(...)t.txt [29]	193.22 μs	3.832 μs	3.935 μs	191.47 μs	1.01	0.03
FileInfo_TryCatch	\10.(...)t.txt [29]	191.04 μs	2.153 μs	1.908 μs	190.60 μs	1.00	0.01

Second run with disconnected VPN, so none of network file exists.

Method	fileName	Mean	Error	StdDev	Median	Ratio	RatioSD
File_Exists	C:\TEMP\test.not	29.88 μs	0.577 μs	0.771 μs	29.56 μs	1.00	0.00
PathFileExists	C:\TEMP\test.not	30.44 μs	0.445 μs	0.372 μs	30.31 μs	1.01	0.03
FileInfo	C:\TEMP\test.not	30.15 μs	0.551 μs	0.736 μs	29.82 μs	1.01	0.03
FileInfo_TryCatch	C:\TEMP\test.not	29.94 μs	0.122 μs	0.108 μs	29.94 μs	0.99	0.03
File_Exists	C:\TEMP\test.txt	46.00 μs	0.651 μs	0.697 μs	45.79 μs	1.00	0.00
PathFileExists	C:\TEMP\test.txt	47.36 μs	0.213 μs	0.166 μs	47.32 μs	1.03	0.02
FileInfo	C:\TEMP\test.txt	46.15 μs	0.262 μs	0.219 μs	46.13 μs	1.00	0.02
FileInfo_TryCatch	C:\TEMP\test.txt	46.06 μs	0.186 μs	0.156 μs	46.07 μs	1.00	0.02
File_Exists	J:\test.not	192,579.07 μs	24,979.846 μs	68,801.750 μs	163,922.15 μs	1.00	0.00
PathFileExists	J:\test.not	90,708.63 μs	6,388.267 μs	17,487.777 μs	85,626.45 μs	0.51	0.16
FileInfo	J:\test.not	191,399.02 μs	18,261.754 μs	50,603.234 μs	172,489.40 μs	1.08	0.40
FileInfo_TryCatch	J:\test.not	192,275.34 μs	15,548.226 μs	43,342.240 μs	176,359.63 μs	1.09	0.39
File_Exists	Z:\test.not	734.13 μs	50.053 μs	143.611 μs	731.10 μs	1.00	0.00
PathFileExists	Z:\test.not	207.38 μs	3.918 μs	3.272 μs	208.13 μs	0.27	0.04
FileInfo	Z:\test.not	408.34 μs	7.726 μs	9.198 μs	407.63 μs	0.55	0.09
FileInfo_TryCatch	Z:\test.not	426.86 μs	8.530 μs	14.252 μs	423.69 μs	0.55	0.10
File_Exists	Z:\test.txt	423.64 μs	8.192 μs	7.663 μs	422.04 μs	1.00	0.00
PathFileExists	Z:\test.txt	206.42 μs	3.919 μs	5.493 μs	205.68 μs	0.49	0.02
FileInfo	Z:\test.txt	418.75 μs	8.126 μs	15.655 μs	416.72 μs	0.96	0.04
FileInfo_TryCatch	Z:\test.txt	410.17 μs	8.149 μs	12.198 μs	412.30 μs	0.95	0.04
File_Exists	\10.(...)t.not [29]	2,105.58 μs	105.539 μs	304.503 μs	2,065.60 μs	1.00	0.00
PathFileExists	\10.(...)t.not [29]	860.60 μs	16.776 μs	23.517 μs	862.48 μs	0.41	0.07
FileInfo	\10.(...)t.not [29]	1,613.70 μs	31.959 μs	75.954 μs	1,600.27 μs	0.78	0.11
FileInfo_TryCatch	\10.(...)t.not [29]	1,607.34 μs	14.477 μs	12.089 μs	1,603.82 μs	0.76	0.12
File_Exists	\10.(...)t.txt [29]	1,609.93 μs	30.897 μs	41.247 μs	1,597.26 μs	1.00	0.00
PathFileExists	\10.(...)t.txt [29]	871.10 μs	15.604 μs	13.030 μs	875.64 μs	0.54	0.01
FileInfo	\10.(...)t.txt [29]	1,596.07 μs	31.785 μs	34.009 μs	1,596.91 μs	0.99	0.03
FileInfo_TryCatch	\10.(...)t.txt [29]	1,612.69 μs	23.002 μs	19.208 μs	1,607.73 μs	1.00	0.03