c++ find any string from a list in another string - c++

Question

What options do I have to find any string from a list in another string ?
With s being an std::string, I tried
s.find("CAT" || "DOG" || "COW" || "MOUSE", 0);
I want to find the first one of these strings and get its place in the string ; so if s was "My cat is sleeping\n" I'd get 3 as return value.
boost::to_upper(s);
was applied (for those wondering).

Answer 1

You can do this with a regex.
I don't think there's a way to get the position of a match directly, so first you have to search for the regex, and if there is a match you can search for that string. Like this:
#include <iostream>
#include <string>
#include <regex>
using namespace std;
int main() {
string s = "My cat is sleeping\n";
smatch m;
regex animal("cat|dog|cow|mouse");
if (regex_search (s,m,animal)) {
cout << "Match found: " << m.str() << endl;
size_t match_position = s.find(m.str());
// In this case it is always true, but in general you might want to check
if (match_position != string::npos) {
cout << "First animal found at: " << match_position << endl;
}
}
return 0;
}

Answer 2

You may convert your search cases to a DFA. It is the most efficient way of doing it.
states:
nil, c, ca, cat., d, do, dog., co, cow., m, mo, mou, mous, mouse.
transition table:
state | on | goto
nil | c | c
nil | d | d
nil | m | m
c | a | ca
c | o | co
d | o | do
m | o | mo
ca | t | cat.
co | w | cow.
do | g | dog.
mo | u | mou
mou | s | mous
mous | e | mouse.
* | * | nil
You may express this using a lot of intermediary functions. Using a lot of switches. Or using enum to represent states and a mapping to represent the transitions.
If your test case list is dynamic or grows too big, then a manually hardcoding the states will nor suffice for you. However, as you can see, the rule to make the states and the transitions is very simple.