the given path format is not supported; streamwriter


Below are the Stacktrace;

  Message=The given path's format is not supported.
   at System.Security.Permissions.FileIOPermission.EmulateFileIOPermissionChecks(String fullPath)
   at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)
   at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access)
   at EntryLog.Handlers.StreamEntryLogs.StreamWritter(String log, String foldername) in C:\Users\JNyingi\source\repos\EntryLog\EntryLog\Handlers\StreamEntryLogs.cs:line 31
   at EntryLog.EntryLog.LogWarning(String Warning) in C:\Users\JNyingi\source\repos\EntryLog\EntryLog\EntryLog.cs:line 55
   at EntryLogConsoleTest.Program.Main(String[] args) in C:\Users\JNyingi\source\repos\EntryLogConsoleTest\EntryLogConsoleTest\Program.cs:line 21

  This exception was originally thrown at this call stack:
    System.IO.FileStream.Init(string, System.IO.FileMode, System.IO.FileAccess, int, bool, System.IO.FileShare, int, System.IO.FileOptions, Microsoft.Win32.Win32Native.SECURITY_ATTRIBUTES, string, bool, bool, bool)
    System.IO.FileStream.FileStream(string, System.IO.FileMode, System.IO.FileAccess)
    EntryLog.Handlers.StreamEntryLogs.StreamWritter(string, string) in StreamEntryLogs.cs
    EntryLog.EntryLog.LogWarning(string) in EntryLog.cs
    EntryLogConsoleTest.Program.Main(string[]) in Program.cs

The exception is coming about from the following lines;

string filePath = System.IO.Path.Combine(EntryLog.LogPath.AbsolutePath, currentTimeFilename + " - " + $"{foldername}.log");

var fileStreamer = new FileStream(filePath, FileMode.OpenOrCreate, FileAccess.Write);
var streamWriter = new StreamWriter(fileStreamer);

The LogPath is obtained by this method;

LogPath = new Uri(Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().Location)); 

I have tried all manner of debugging but it always throws the above exception at StreamWriter. Kindly assist me in resolving this. I'm using 4.5.2 .net Framework


The file path in question is this; C:\Users\JNyingi\source\repos\EntryLogConsoleTest\EntryLogConsoleTest\bin\Debug


string currentTimeFilename = DateTime.Now.ToString("yyyy-MM-dd HH:mm");

string foldername = "Log"

asked on Stack Overflow Jan 24, 2020 by John Nyingi • edited Jan 24, 2020 by John Nyingi

2 Answers


the problem is the : in your filename

string currentTimeFilename = DateTime.Now.ToString("yyyy-MM-dd HH:mm"); 

Change it to - or _ or even a . for example and the error disappears

string currentTimeFilename = DateTime.Now.ToString("yyyy-MM-dd HH_mm"); 
answered on Stack Overflow Jan 24, 2020 by Mong Zhu

Using ILSpy you can find that the code of the method EmulateFileIOPermissionChecks (which raises the NotSupportedException) is:

internal static void EmulateFileIOPermissionChecks(string fullPath)
    if (AppContextSwitches.UseLegacyPathHandling || !PathInternal.IsDevice(fullPath))
        if (PathInternal.HasWildCardCharacters(fullPath))
            throw new ArgumentException(Environment.GetResourceString("Argument_InvalidPathChars"));
        if (PathInternal.HasInvalidVolumeSeparator(fullPath))
            throw new NotSupportedException(Environment.GetResourceString("Argument_PathFormatNotSupported"));

So your path contains invalid chars.


If in your settings hours - minutes separator is a colon (see your datetime formatted string), please consider that ':' cannot be used in a path, but after driver letter.

answered on Stack Overflow Jan 24, 2020 by Il Vic • edited Jan 24, 2020 by Il Vic

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