CodeQL library for C/C++
codeql/cpp-all 0.12.10 (changelog, source)

Member predicate TextLiteral::getANonStandardEscapeSequence

Gets a non-standard escape sequence that appears in the character or string literal. This is one that has the form of an escape sequence but is not one of the valid types of escape sequence in the C++ Standard.

string getANonStandardEscapeSequence(int occurrence, int offset)