Non-encoded control characters and whitespace characters are often injected in the source code because of a bad manipulation. They are either invisible or difficult to recognize, which can result in bugs when the string is not what the developer expects. If you actually need to use a control character use their encoded version (ex: ASCII \n,\t,…​ or Unicode U+000D, U+0009,…​).

This rule raises an issue when the following characters are seen in a literal string:

• ASCII control character. (character index < 32 or = 127)
• Unicode whitespace characters.
• Unicode C0 control characters
• Unicode characters U+200B, U+200C, U+200D, U+2060, U+FEFF, U+2028, U+2029

No issue will be raised on the simple space character. Unicode U+0020, ASCII 32.

Noncompliant Code Example

string tabInside = "A	B";  // Noncompliant, contains a tabulation
string zeroWidthSpaceInside = "foo​bar"; // Noncompliant, it contains a U+200B character inside
Console.WriteLine(zeroWidthSpaceInside); // Prints "foo?bar"

Compliant Solution

string tabInside = "A\tB";  // Compliant, uses escaped value
string zeroWidthSpaceInside = "foo\u200Bbar";  // Compliant, uses escaped value
Console.WriteLine(zeroWidthSpaceInside); // Prints "foo?bar"

Exceptions

Verbatim string literals have no escape character mechanism.