Removing hidden characters from within strings

Question

My problem:

I have a .NET application that sends out newsletters via email. When the newsletters are viewed in outlook, outlook displays a question mark in place

Answer 1

I usually use this regular expression to replace all non-printable characters.

By the way, most of the people think that tab, line feed and carriage return are non-printable characters, but for me they are not.

So here is the expression:

string output = Regex.Replace(input, @"[^\u0009\u000A\u000D\u0020-\u007E]", "*");

• ^ means if it's any of the following:
• \u0009 is tab
• \u000A is linefeed
• \u000D is carriage return
• \u0020-\u007E means everything from space to ~ -- that is, everything in ASCII.

See ASCII table if you want to make changes. Remember it would strip off every non-ASCII character.

To test above you can create a string by yourself like this:

    string input = string.Empty;

    for (int i = 0; i < 255; i++)
    {
        input += (char)(i);
    }