Regex_match doesn't match in a file - regex

Question

I want to recognize some lines in a text file using regex, but regex_match doesn't match any line, even if I use regex patron(".*")
string dirin = "/home/user/in.srt";
string dirout = "/home/user/out.srt";
ifstream in(dirin.c_str());
ofstream out(dirout.c_str());
string line;
// regex patron("(\\d{2}):(\\d{2}):(\\d{2}),(\\d{3})\\s-->\\s(\\d{2}):(\\d{2}):(\\d{2}),(\\d{3})");
regex patron(".*");
smatch m;
while (getline(in, line)) {
if (regex_match(line, m, patron)) {
out << "ok";
};
out << line;
}
in.close();
out.close();
The code always print the string line in the out.srt file, but never the string "ok" inside the if (regex_match(line, m, patron)).
I'm testing it with the following lines
1
00:01:00,708 --> 00:01:01,800
You look at that river
2
00:01:02,977 --> 00:01:04,706
gently flowing by.
3
00:01:06,213 --> 00:01:08,238
You notice the leaves

Answer 1

Note that getline() reads a line with a trailing carriage return CR symbol, and note that ECMAScript . pattern does not match CR symbol considering it an end of line symbol.
regex_match requires that a whole string matches the pattern.
Thus, you need to account for an optional carriage return at the end of the pattern. You can do it by appending \r? or \s* at the end of the pattern:
regex patron("(\\d{2}):(\\d{2}):(\\d{2}),(\\d{3})\\s-->\\s(\\d{2}):(\\d{2}):(\\d{2}),(\\d{3})\\s*");
or
regex patron(".*\\s*");
Also, consider using raw string literals if your C++ version allows it:
regex patron(R"((\d{2}):(\d{2}):(\d{2}),(\d{3})\s-->\s(\d{2}):(\d{2}):(\d{2}),(\d{3})\s*)");