If you feel it to be worth make your small DSL (or maybe it already exists) so you can do (java):

// ^("(?:[^"]|\")*"|-?[0-9]+(?:.[0-9]+)?)$
// @formatter:off
Pattern pattern = Patterning.start() // ^
    .group()
    .lookahead()
        ...
        .set("0-9").plus()
        .string("E=m.c^2") // Q ... E
    .lookaheadEnd()
    .groupEnd();
    .end()                               // $
    .build();
// @formatter:on

class Patterning { ... }

Though most people know regex; or at least it is worth learning regex, if only to do powerfull replaces in the editor.

In C++, use raw string literals (added in C++11). Nothing between the delimiter sequences is treated as an escape:

const char *regex = R"-regexp-(^("(?:[^"]|\")*"|-?[0-9]+(?:.[0-9]+)?)$)-regexp-";

in this case the delimiters are the literal strings -regexp-( and )-regexp-

Use Unicode character escapes instead of literals. For example:

• Java

  boolean b = Pattern.matches("u0022", '"');
  

• JavaScript

  /u0022/.test('"');
  

• Perl

  '"' =~ /N{U+0022}/;
  

In addition, strings that are compiled to regular expressions can use line breaks for added clarity:

• Java

  boolean phone_mask = Pattern.matches("^[^0-9]*"/* Optional non-numeric characters */ +
                          "\+9{3}" /* Followed by a plus sign and three nines */ +
                          "\s9"    /* Followed by a space and one nine */  +
                          "\s9{3}" /* Followed by a space and three nines */ +
                          "\s9{4}" /* Followed by a space and four nines */ +
                          "$", "Phone: +999 9 999 9999");
  

• JavaScript

  var phone_mask = RegExp("^[^0-9]*"/* Optional non-numeric characters */ +
                          "\+9{3}" /* Followed by a plus sign and three nines */ +
                          "\s9"    /* Followed by a space and one nine */  +
                          "\s9{3}" /* Followed by a space and three nines */ +
                          "\s9{4}" /* Followed by a space and four nines */ +
                          "$").test("Phone: +999 9 999 9999");
  

References

• Character Escapes in Regular Expressions | Microsoft Docs
• Java Regex Examples Matching Characters
• perlrequick – perldoc.perl.org
• Java literals
• pcreunicode specification
• Maintaining Regular Expressions

Write a program that interprets and escapes your regexps for you.
You can either use this to generate the code needed to paste into your source or have it work on the fly having your regexp in a separate file.

For the file version, a big downside is: not having your logic with your source.