C ++正则表达式排除双引号不起作用

Question

I am considering input files with lines like

"20170103","MW JANE DOE","NL01 INGB 1234 5678 90","NL02 INGB 1234 5678 90","GT","Af","12,34","Internetbankieren","Mededeling_3"
"20170102","MW JANE DOE","NL01 INGB 1234 5678 90","NL02 INGB 1234 5678 90","GT","Af","12,34","Internetbankieren","Mededeling_2"
"20170101","MW JANE DOE","NL01 INGB 1234 5678 90","NL02 INGB 1234 5678 90","GT","Af","12,34","Internetbankieren","Mededeling_1"

. I want to get the separate strings WITHOUT THE DOUBLE QUOTES and store them in std::vector<std::string> . So, for instance, I want to have 20170101 , MW JANE DOE , NL01 INGB 1234 5678 90 , NL02 INGB 1234 5678 90 , GT , Af , 12,34 , Internetbankieren , and Mededeling_1 as a result.

I try to do so with the code

std::regex re("\"(.*?)\"");
std::regex_iterator<std::string::iterator> it (line.begin(),line.end(),re);
std::regex_iterator<std::string::iterator> end;
std::vector<std::string> lineParts;
std::string linePart="";

// Split 'line' into line parts and save these in the vector 'lineParts'.
while (it!=end)
{
    linePart=it->str();
    std::cout<<linePart<<std::endl; // Print substring.
    lineParts.push_back(linePart);
    ++it;
}

However, the double quotes are still included in the elements of lineParts , even though I used the regex "\\"(.*?)\\"" so that supposedly only the part within the double quotes is saved, and not the double quotes themselves.

What am I doing wrong?

Answer 1

You have a pattern with a capturing group . So, when your regex finds a match, the double quotes are part of the whole match value (that is stored in the [0] th element), but the captured part is stored in the [1] th element.

So, you just need to access capturing group #1 contents:

linePart=it->str(1);

See regular-expressions.info Finding a Regex Match :

When the function call returns true, you can call the str() , position() , and length() member functions of the match_results object to get the text that was matched, or the starting position and its length of the match relative to the subject string. Call these member functions without a parameter or with 0 as the parameter to get the overall regex match. Call them passing 1 or greater to get the match of a particular capturing group. The size() member function indicates the number of capturing groups plus one for the overall match. Thus you can pass a value up to size()-1 to the other three member functions.

Answer 2

As others have said, regex_iterator::operator-> returns a match_results and match_results::str is defaulted to 0:

The first sub_match (index 0 ) contained in a match_result always represents the full match within a target sequence made by a regex , and subsequent sub_matches represent sub-expression matches corresponding in sequence to the left parenthesis delimiting the sub-expression in the regex

So the problem with your code is you're not using linePart = it->str(1) .

A better solution would be to use a regex_token_iterator . With whitch you could just use your re to directly initialize lineParts :

vector<string> lineParts { sregex_token_iterator(cbegin(line), cend(line), re, 1), sregex_tokent_iterator() };

---

But I'd just like to point out that c++14 introduced quoted does exactly what you're trying to do here, and more (it even handles escaped quotes for you!) It'd just be a shame not to use it.

You probably are already getting your input from a stream, but just in the case you're not you'd need to initialize an istringstream , for the purposes of example I'll call mine: line . Then you can use quoted to populate lineParts like this:

for(string linePart; line >> quoted(linePart); line.ignore(numeric_limits<streamsize>::max(), ',')) {
    lineParts.push_back(linePart);
}

Live Example