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 filen";

    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 jdoe@machine.example
To: Mary Smith mary@example.net
Subject: Saying Hello
Date: Fri,21 Nov 1997 09:55:06 -0600
Message-ID: <1234@local.machine.example>

This is a message just to say hello.

So,“Hello”.

From: Joe Q. Public john.q.public@example.com
To: Mary Smith <@machine.tld:mary@example.net>,jdoe@test .example
Date: Tue,1 Jul 2003 10:52:37 +0200
Message-ID: <5678.21-Nov-1997@example.com>

Hi everyone.

To: “Mary Smith: Personal Account” smith@home.example
From: John Doe jdoe@machine.example
Subject: Re: Saying Hello
Date: Fri,21 Nov 1997 11:00:00 -0600
Message-ID: abcd.1234@local.machine.tld
In-Reply-To: <3456@example.net>
References: <1234@local.machine.example> <3456@example.net>

This is a reply to your reply.

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输出结果