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Remove MAX_PATH Limitations

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As technology advances, applications increase their complexity. As a result, installers deploy more and more files and folders to the install directories.  Software developers should not rely on the Window’s MAX_PATH constant when developing their applications. Many Windows APIs don’t support file paths that are longer than MAX_PATH in length directly. However, they do support these files under some rules. I recommend you to follow this guideline when working with file APIs.

1 : Never use MAX_PATH constant in the code. Most of us tend to allocate buffers with a magic number. However, this is not a good practice as it may introduce security threats and reduce the robustness of program. Instead, use a vector object as a buffer. You will have the power of changing its size based on your file path length.

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2 : Prepend [\\?\](file://\\?\) characters to the file paths that are longer than MAX_PATH. Most Windows APIs support file paths that are longer than MAX_PATH in length IFF file path contains [\\?\](file://\\?\) prefix. However, do not prepend this prefix to the file paths that are less than MAX_PATH in length as prepending this prefix causes APIs to skip some validations that are valuable for the program.

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3: Of course, do not use Windows APIs that do not support file paths that are longer than MAX_PATH in length. Some APIs fail even if you prepend the [\\?\](file://\\?\) prefix to the file path. SHFileOperation is one example to these APIs.

4: Wrap the Windows APIs to your own functions so that you will have one entry to control if you need to make any change to the API. 

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5: Write unit test! To ensure that your code works fine for any file paths with any lengths, write your unit test and validate your code.

Comments

  • Anonymous
    December 03, 2010
    Folks, don't forget that creating file paths that don't meet the Win32 PATH length limitions means that those files cannot be accessed by Windows explorer and many common programming techniques.  The .NET liberary also limits path links to MAX_PATH, so this can cause problems in managed code as well.   There are valid times to use the "?" prefix, but understand the caveats and limitions before you do so.

  • Anonymous
    August 24, 2014
    Hello Long Path Tool is the most appropriate program to sort out such issues