std::regex_search

#include <cstddef>
#include <iostream>
#include <regex>
#include <string>
 
int main()
{
 std::string lines[] = {"Roses are #ff0000",
 "violets are #0000ff",
 "all of my base are belong to you"};
 
 std::regex color_regex("#([a-f0-9]{2})"
 "([a-f0-9]{2})"
 "([a-f0-9]{2})");
 
 // simple match
 for (const auto& line : lines)
 std::cout << line << ": " << std::boolalpha
 << std::regex_search(line, color_regex) << '\n';
 std::cout << '\n';
 
 // show contents of marked subexpressions within each match
 std::smatch color_match;
 for (const auto& line : lines)
 if (std::regex_search(line, color_match, color_regex))
 {
 std::cout << "matches for '" << line << "'\n";
 std::cout << "Prefix: '" << color_match.prefix() << "'\n";
 for (std::size_t i = 0; i < color_match.size(); ++i) 
 std::cout << i << ": " << color_match[i] << '\n';
 std::cout << "Suffix: '" << color_match.suffix() << "\'\n\n";
 }
 
 // repeated search (see also std::regex_iterator)
 std::string log(R"(
 Speed:	366
 Mass:	35
 Speed:	378
 Mass:	32
 Speed:	400
	Mass:	30)");
 std::regex r(R"(Speed:\t\d*)");
 for (std::smatch sm; regex_search(log, sm, r);)
 {
 std::cout << sm.str() << '\n';
 log = sm.suffix();
 }
 
 // C-style string demo
 std::cmatch cm;
 if (std::regex_search("this is a test", cm, std::regex ("test"))) 
 std::cout << "\nFound " << cm[0] << " at position "
 << cm.prefix().length() << '\n';
}

Roses are #ff0000: true
violets are #0000ff: true
all of my base are belong to you: false
 
matches for 'Roses are #ff0000'
Prefix: 'Roses are '
0: #ff0000
1: ff
2: 00
3: 00
Suffix: ''
 
matches for 'violets are #0000ff'
Prefix: 'violets are '
0: #0000ff
1: 00
2: 00
3: ff
Suffix: ''
 
Speed:	366
Speed:	378
Speed:	400
 
Found test at position 10