C++ regex_replace issue

Question

Why this code does not replace the 'Mozilla/5.0' to 'My User Agent'?

The Regex works fine in Notepad++ but does not work in my console app.

#include <regex>
#include <string>
using namespace std;

int _tmain(int argc, _TCHAR* argv[])
{
    string header = 
"GET / HTTP/1.1\r\n\
Host: com.com\r\n\
User-Agent: Mozilla/5.0\r\n\
Connection: keep-alive";

    tr1::regex rx("^(User-Agent:).+$", regex_constants::icase);
    header = regex_replace(header, rx, "$1 My User Agent", regex_constants::format_first_only);

    return 0;
}

What compiler are you using? regex C++11 was not fully supported until very recently. It may be that Notepad++ is using a different compiler from your console (this is in case you don't get a compilation error) — vsoftco
– vsoftco, Commented May 11, 2014 at 4:55
Are you getting an error when compiling with VS? Or nothing happens? — vsoftco
– vsoftco, Commented May 11, 2014 at 4:59
When you say "works fine in Notepad++", you mean you are compiling a program with Notepad++ and it works? Or you are using the regex in Notepad++? — vsoftco
– vsoftco, Commented May 11, 2014 at 5:17

Ulugbek Umirov · Accepted Answer · 2014-05-11 05:22:24Z

5

The problem is that ^ means beginning of string, not beginning of line. You can use the following regex, which works fine:

((?:^|\r\n)User-Agent:).+(?=$|\r\n)

Regular expression visualization

answered May 11, 2014 at 5:22

Ulugbek Umirov

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