string FileSystem::GetStringBetweenExpressions(const string& str, const string& firstExpression, const string& secondExpression)
{
// ("The quick brown fox", "The ", " brown") -> "quick"
regex base_regex(firstExpression + "(.*)" + secondExpression);
smatch base_match;
if (regex_search(str, base_match, base_regex))
{
// The first sub_match is the whole string; the next
// sub_match is the first parenthesized expression.
if (base_match.size() == 2)
{
return base_match[1].str();
}
}
return str;
}
int main()
{
// Simple regular expression matching
std::string fnames[] = {"foo.txt", "bar.txt", "baz.dat", "zoidberg"};
std::regex txt_regex("[a-z]+\\.txt");
for (const auto &fname : fnames) {
std::cout << fname << ": "
<< std::regex_match(fname, txt_regex) << '\n';
}
// Extraction of a sub-match
std::regex base_regex("([a-z]+)\\.txt");
std::smatch base_match;
for (const auto &fname : fnames) {
if (std::regex_match(fname, base_match, base_regex)) {
// The first sub_match is the whole string; the next
// sub_match is the first parenthesized expression.
if (base_match.size() == 2) {
std::ssub_match base_sub_match = base_match[1];
std::string base = base_sub_match.str();
std::cout << fname << " has a base of " << base << '\n';
}
}
}
// Extraction of several sub-matches
std::regex pieces_regex("([a-z]+)\\.([a-z]+)");
std::smatch pieces_match;
for (const auto &fname : fnames) {
if (std::regex_match(fname, pieces_match, pieces_regex)) {
std::cout << fname << '\n';
for (size_t i = 0; i < pieces_match.size(); ++i) {
std::ssub_match sub_match = pieces_match[i];
std::string piece = sub_match.str();
std::cout << " submatch " << i << ": " << piece << '\n';
}
}
}
}
