如何使用正则表达式检测无效的C转义字符串？

Question

I would like to find a regular expression (regex) that does detect if you have some invalid escapes in a C double quoted escaped string (where you can find double quotes only escaped).

I consider valid \\\\ \\n \\r \\" (the test string is using ")

A partial solution to this is to use (?<!\\\\)\\\\[^\\"\\\\nr] but this one fails to detect bad escapes like \\\\\\ .

Here is a test string that I use to test the matching:

...\\n...\\\\b...\\"...\\\\\\\\...\\\\\\E...\\...\\\\\\...\\\\\\\\\\..."...\\E...

The expression should match the last 6 blocks as invalid, the first 4 are valid. The problem is that my current version does find only 2/5 errors.

Answer 1

(?:^|[^\\])(?:\\\\)*((?:\"|\\(?:[^\"\\nr]|$)))

That's the start of a string, or something that's not a backslash. Then some (possibly zero) properly escaped backslashes, then either an unescaped " or another backslash; if it's another backslash, it must be followed by something that is neither " , \\ , n , nor r , or the end of the string.

The incorrect escape is captured for you as well.

Answer 2

Try this regular expression:

^(?:[^\\]+|\\[\\rn"])*(\\(?:[^\\rn"]|$))

If you have a match, you have an invalid escape sequence.