How to use regex_search to get the a line of text from two different .txt files

Question

I'm trying to use this regex pattern Subject: [\a-zA-Z_0-9]+ in c++ to get this line of text from two different files one being this:

Message-ID: <..>
Subject: AAAI-22 General Information
MIME-Version: 1.0
Content-Type: multipart/alternative; ..
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

and the other being

Subject: Re: Possible need for … 240
Thread-Topic: Possible need for printout for .. 240

however, the regex pattern matches:

Subject: AAAI-22 General Information MIME-Version: 1.0
Content-Type: multipart/alternative; ..Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

for the first text file and for the second file the pattern matches

Subject: Re: Possible need for 

All I want my regex pattern to search for and print out is the Subject: and whatever else is in that line and nothing else. How can I do that using regex_search and regex_replace patterns?

Answer 1

You can use this regex pattern to search for Subject line

"Subject: .+"

Explanation:

• Subject: matches the characters Subject: literally (case sensitive).

• .matches any character (except for line terminators)

• + matches the previous token between one and unlimited times