#include <iostream>
#include <fstream>
#include <string>
#include <regex>

using namespace std;
int main()
{

    regex r1("(.*\\blecture\\b.*)");
    regex r2("(.* practice.*)");
    regex r3("(.* laboratory practice.*)");
    smatch base_match;
    int lecture = 0;
    int prakt = 0;
    int lab = 0;
    string name = "schedule.txt";
    ifstream fin;
    fin.open(name);
    if (!fin.is_open()) {
        cout << "didint open ";
    }
    else {
        string str;
        while (!fin.eof()) {
            str = "";
            getline(fin, str);
            cout << str << endl;

            if (regex_match(str, base_match, r1)) {
                lecture  ;
            }
            if (regex_match(str, base_match, r2)) {
                prakt  ;
            }
            if (regex_match(str, base_match, r3)) {
                lab  ;
            }
        }
    }
    cout << "The number of lectures: " << lecture << "\n";
    cout << "The number of practices: " << prakt << "\n";
    cout << "[The number of laboratory work][1]: " << lab << "\n";

    fin.close();
}

In this program, I need to count the number of lectures, practice and laboratory work per week using regular expressions. I have got a text file, which you can see on the screen. But for lectures and practice, it doesn't work right.

enter image description here

CodePudding user response：

You need the number of times each regex matches. C has std::sregex_iterator for performing multiple regex matches over a string. That means you can do the following:

for (auto it = std::sregex_iterator{str.cbegin(), str.cend(), r1}; it != std::sregex_iterator{}; it  ) {
  lecture  ;
}

If you want to get really fancy you can even do it in one go:

auto it = std::sregex_iterator{str.cbegin(), str.cend(), r1};
lecture  = std::distance(it, std::sregex_iterator{});

Alternatively, you can call std::regex_search several times, starting from the end offset of the previous match (or 0 for the first).

EDIT: as remarked in the comments, this assumes that your regexes are suitable to incremental matching. Yours eat the whole string (presumably because regex_match is anchored whereas regex_search/regex_iterator are not), so you need to at least change your regular expression definitions to the following:

regex r1("\\blecture\\b");
regex r2(" practice");
regex r3(" laboratory practice");

... and of course every match for r3 is also a match for r2, but I leave that for you.