C++ split string line by line using std::regex

Question

I use this function to split the string:

std::vector<std::string> splitString(const std::string& stringToSplit, const std::string& regexPattern)
{
    std::vector<std::string> result;

    const std::regex rgx(regexPattern);
    std::sregex_token_iterator iter(stringToSplit.begin(), stringToSplit.end(), rgx, -1);

    for (std::sregex_token_iterator end; iter != end; ++iter)
    {
        result.push_back(iter->str());
    }

    return result;
}

Now, if I want to split a string line by line (say, I have read a file content into a single variable), I do this:

auto vec = splitString(fileContent, "\\n");

On Windows, I get this:

line 1 \r
line 2 \r

This happens because Windows line ending is determined with \r\n. I have tried to use $, but again without success. What is the right way to capture line endings in Windows, too?

Use [\\r\\n]+. auto vec = splitString(fileContent, "[\\r\\n]+"); — Wiktor Stribiżew
– Wiktor Stribiżew, Commented May 5, 2015 at 10:41
Since the \r and \n are line separators, I think it will run on all OSes. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented May 5, 2015 at 10:43
Please let me know if the regex works for you, then I could post it as answer. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented May 5, 2015 at 11:01
@Narek: Yes it will work for these systems (all use LF as newline). But unfortunately it will not work on the ATARI 800 :) — Casimir et Hippolyte
– Casimir et Hippolyte, Commented May 5, 2015 at 11:09

Wiktor Stribiżew · Accepted Answer · 2015-05-05 12:46:17Z

3

On Linux/Unix, OS X, iOS, Android OSes, line separators are either \r, or \n, or a combination of them. So, the most efficient way to capture them all is placing into a character class and use the + quantifier.

Thus, [\\r\\n]+ should "do the trick":

auto vec = splitString(fileContent, "[\\r\\n]+");

EDIT:

As @FabioFracassi mentions, this will remove empty lines. If empty lines should be preserved in the output, you can use

auto vec = splitString(fileContent, "(?:\\r\\n|\\r|\\n)");

The alternative list is starting with the longest option, since regular expressions are processed from left to right (at least, by default).

edited May 5, 2015 at 12:46

answered May 5, 2015 at 11:44

Wiktor Stribiżew

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2 Comments

Fabio Fracassi Over a year ago

won't that have inconsistent behavior on (consecutive) empty lines?

Wiktor Stribiżew Over a year ago

That depends on whether empty lines must be present in the resulting array. It is true that in case empty lines should be preserved, the regex must be "(?:\\r\\n|\\r|\\n)".

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