My code with regular expressions for file doesn't run properly - c++

Question

#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

Answer 1

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.