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How do you handle long file paths (over 260 characters) in .NET Framework and .NET Core?

ICSM Computer 1791 16 May 2025

Ask by ICSM Computer

Updated 16 May 2025

1 Answers

ICSM Computer 16 May 2025

Handling long file paths (over 260 characters) requires different approaches in .NET Framework vs .NET Core due to historical limitations.

Why the 260 Character Limit?

Windows historically imposed a MAX_PATH limit of 260 characters. In .NET Framework, this limit is enforced unless you use special workarounds. .NET Core and .NET 5+ have better support for long paths by default.

.NET Framework (≤ 4.6.2)

Problem:

By default, paths longer than 260 characters cause an error like:

System.IO.PathTooLongException

Workaround:

Use UNC (long path) prefix: \\?\ before absolute paths.

string longPath = @"\\?\C:\very\long\path\to\your\file.txt";
File.ReadAllText(longPath);

Requirements:

Must use full (absolute) paths.
Works only with local paths, not relative paths.
Limited support in many .NET APIs.

.NET Core / .NET 5+ / .NET 6+

.NET Core and .NET 5+ fully support long paths without requiring \\?\ if the OS supports it and it's enabled.

Ensure Windows long paths are enabled:

Open gpedit.msc
Navigate to:
Computer Configuration > Administrative Templates > System > Filesystem
Enable: Enable Win32 long paths

Or modify registry:

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\FileSystem]
"LongPathsEnabled"=dword:00000001

Then use normally:

string path = @"C:\some\very\long\directory\structure\...file.txt";
File.WriteAllText(path, "data");

Tips

Prefer .NET Core or later for better long path support.
Avoid long path issues by keeping directory structures flat when possible.
Use Path.GetFullPath() to debug unexpected length problems.

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