正则表达式练习——将文本中的日期格式化为标准格式

//匹配文本中的日期，并将日期转换为标准格式
void dateFormatEx(void)
{
    ifstream in(".\\chapter.23.4.1.in",ios::binary);
    if (!in)cerr << "no file\n";

    boost::regex pat("([\\d]+) ([\\w]+) ([\\d]+)");
    cout << "pattern: " << pat << '\n';

    int lineno = 0;
    string line;
    while (getline(in,line))
    {
        ++lineno;
        boost::smatch matches;
        if (boost::regex_search(line,matches,pat))
        {
            string day = matches[1];
            string mon = matches[2];
            string year = matches[3];
            line = boost::regex_replace(line,pat,year+"/"+mon+"/"+day);
        }
        cout << line << endl;
    }
}

文本语料
xxx

xxx

From: John Doe [e-mail]
To: Mary Smith [e-mail]
Subject: Saying Hello
Date: Fri,21 Nov 1997 09:55:06 -0600
Message-ID: <[e-mail]>

This is a message just to say hello.

So,“Hello”.

From: Joe Q. Public [e-mail]
To: Mary Smith <@machine.tld:[e-mail]>,jdoe@test .example
Date: Tue,1 Jul 2003 10:52:37 +0200
Message-ID: <[e-mail]>

Hi everyone.

To: “Mary Smith: Personal Account” [e-mail]
From: John Doe [e-mail]
Subject: Re: Saying Hello
Date: Fri,21 Nov 1997 11:00:00 -0600
Message-ID: [e-mail]
In-Reply-To: <[e-mail]>
References: <[e-mail]> <[e-mail]>

This is a reply to your reply.

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输出结果