CODEWITHSUNDEEP
c++regex
alexbuisson
alexbuisson

Reputation: 8499

regex_match doesn't find any matching

I tested the RegEx [BCGRYWbcgryw]{4}\[\d\] on that site and it seems ok to find match in the following BBCC[0].GGRY[0].WWWW[soln]. It match with BBCC[0] and GGRY[0].

But when I tried to code and debug that matching, the smvalue stay empty. 

    regex r("[BCGRYWbcgryw]{4}\\[\\d\\]");
string line; in >> line;
smatch sm;
regex_match(line, sm, r, regex_constants::match_any);
copy(boost::begin(sm), boost::end(sm), ostream_iterator<smatch::value_type>(cout, ", "));

Where am I wrong ?

Upvotes: 0

Views: 540

Answers (2)

Jonathan Wakely
Jonathan Wakely

Reputation: 171413

If you don't want to match the whole input sequence then use std::regex_search not std::regex_match

#include <iostream>
#include <regex>
#include <iterator>
#include <algorithm>

int main()
{
  using namespace std;
  regex r(R"([BCGRYWbcgryw]{4}\[\d\])");
  string line = "BBCC[0].GGRY[0].WWWW[soln]";
  smatch sm;
  regex_search(line, sm, r, regex_constants::match_any);
  copy(std::begin(sm), std::end(sm), ostream_iterator<smatch::value_type>(cout, ", "));
  cout << endl;
}

N.B. this also uses raw strings to simplify the regular expression.

Upvotes: 1

alexbuisson
alexbuisson

Reputation: 8499

I finally get it work, with () to define a capture group and I use regex_iterator to find all sub-string matching the pattern.

std::regex rstd("(\\[[0-9]\\]\.[BCGRYWbcgryw]{4})");
std::sregex_iterator stIterstd(line.begin(), line.end(), rstd);
std::sregex_iterator endIterstd;

for (stIterstd; stIterstd != endIterstd; ++stIterstd)
{
    cout << " Whole string " << (*stIterstd)[0] << endl;
    cout << " First sub-group " << (*stIterstd)[1] << endl;
}

The output is:

Whole string [0].GGRY
First sub-group [0].GGRY
Whole string [0].WWWW
First sub-group [0].WWWW

Upvotes: 0

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