Question

I have here a string(an input from the user) for a file path. I checked the string so that it will qualify the criteria:

• check for invalid characters for a file path
• will not accept absolute path (\Sample\text.txt)

Invalid characters are:

< > : ” / \ | ? *

I have tried catching these invalid characters in catch clause. It work except for ‘\’. It will accept ‘C:\\Sample\text.txt’ which is an invalid file path.

The following examples should be invalid paths:

• :\text.txt
• :text.txt
• \:text.txt
• \text.txt
• C:\\\text.txt

The ff. is an example of a valid path:

• C:\text.txt

I have been through similar questions posted here but none of them seemed to solve my issue.

What would be the best way to do such check?

Answer 1

You may use Path.GetFullPath, it will throw an exception if the path is invalid. You can have method like:

public static bool IsValidPath(string path)
{
    try
    {
       path = path.Replace(@"\\", ":"); // to cancel out c:\\\\test.text
       string temp = Path.GetPathRoot(path); //For cases like: \text.txt
       if (temp.StartsWith(@"\"))
            return false;
       string pt = Path.GetFullPath(path);
    }
    catch //(Exception NotSupportedException) // catch specific exception here or not if you want
    {
        return false;
    }
    return true;
}

Sample code to test:

List<string> list = new List<string>()
{
    @":\text.txt",
    @":text.txt",
    @"\:text.txt",
    @"\text.txt",
    @"C:\\\text.txt",
    @"C:\text.txt",

};

foreach(string str in list)
{
    Console.WriteLine("Path: {0} is Valid = {1}" ,str,IsValidPath(str));
}

Output:

Path: :\text.txt is Valid = False
Path: :text.txt is Valid = False
Path: \:text.txt is Valid = False
Path: \text.txt is Valid = False
Path: C:\\\text.txt is Valid = False
Path: C:\text.txt is Valid = True