Question

Here is how I’m creating a file:

System.IO.File.Create(Server.MapPath("..") + name + ".html");

But sometimes name has illegal characters, like å, from the swedish alphabet. How to save them? It is possible directly, but I get error when I do it with code.

Answer 1

If the path is user controlled and potentially contains invalid file system characters then you’ll need to ask the user to change the name or normalize out the bad characters in a deterministic way. One method is to replace all invalid characters with say underscore.

public static string NormalizeFileName(string input) {
  var invalid = Path.GetInvalidPathChars();
  var builder = new System.Text.StringBuilder();
  foreach(char c in input) {
    if (invalid.Contains(c)) {
      builder.Append('_');
    } else {
      builder.Append(c);
    }
  }
  return builder.ToString();
}

You could then use this function as follows

var originalName = Server.MapPath("..") + name + ".html";
var normalizedName = NormalizeFileName(originalName);
System.IO.File.Create(normalizedName);

EDIT

As several people pointed out, it’s best practice to use Path.Combine here to combine directory and file names.

var originalName = Path.Combine(Server.MapPath(".."), name + ".html");