scanf regex - C

Question

I needed to read a string until the following sequence is written: x :

(.....)

x

is the new line character and (.....) can be any characters that may include other characters.

scanf allows regular expressions as far as I know, but i can't make it to read a string untill this pattern. Can you help me with the scanf format string?

---

I was trying something like:

char input[50000];
scanf(" %[^(
x
)]", input);

but it doesn't work.

Answer 1

scanf allows regular expressions as far as I know

Unfortunately, it does not allow regular expressions: the syntax is misleadingly close, but there is nothing even remotely similar to the regex in the implementation of scanf. All that's there is a support for character classes of regex, so %[<something>] is treated implicitly as [<something>]*. That's why your call of scanf translates into read a string consisting of characters other than '(', ')', 'x', and ' '.

To solve your problem at hand, you can set up a loop that read the input character by character. Every time you get a ' ', check that

• You have at least three characters in the input that you've seen so far,
• That the character immediately before ' ' is an 'x', and
• That the character before the 'x' is another ' '

If all of the above is true, you have reached the end of your anticipated input sequence; otherwise, your loop should continue.