Question

I need a c# method to encode ampersands if they are not already encoded or part of another encoded epxression

eg

"tom & jill" should become "tom & jill"


"tom & jill" should remain "tom & jill"


"tom € jill" should remain "tom € jill"


"tom <&> jill" should become "tom <&amp;> jill"


"tom &quot;&&quot; jill" should become "tom &quot;&amp;&quot; jill"

Answer 1

This should do a pretty good job:

text = Regex.Replace(text, @"
    # Match & that is not part of an HTML entity.
    &                  # Match literal &.
    (?!                # But only if it is NOT...
      \w+;             # an alphanumeric entity,
    | \#[0-9]+;        # or a decimal entity,
    | \#x[0-9A-F]+;    # or a hexadecimal entity.
    )                  # End negative lookahead.", 
    "&",
    RegexOptions.IgnoreCase | RegexOptions.IgnorePatternWhitespace);