How to convert IP rule like 192.168.*.* into c++ regex

I want to check rules in my file which looks like 192.168.*.* * mean any number. All IPs tested are legal. That's no need to concern special case like 456.123.abc.333.

Now, I want to do this with c++11 regex. But I don't know how to convert match . into regex correctly. I will read rules into string, and try to convert it to regex style by function I defined.
In regex, the match for . is \..

But when I try to do this conversion by my function replace with arguments old_val:. & new_val\\.(for escaping \, I use \\), the rule 192.168.*.* will become 192\\.168\\.*\\.*.

What part of my code need to fix to do this correctly?
Or is there another easier way to do this?

bool check_rule(string CD, string IP){

    fstream firewall;
    firewall.open("./socks.conf");
    string rule;

    while(getline(firewall, rule)){
        stringstream ss(rule);
        string judge, mode, regular;
        ss >> judge >> mode >> regular;

        //check if mode is correct
        if(mode == CD){
        replace(regular, ".", "\\.");
        replace(regular, "*", "\\d");
        cout << "regex :" << regular << endl;
        regex regu_expr(regular);
        smatch m;
        if(regex_match(IP, m, regu_expr)){
            return true;   
        }
        }
    }
    return false;

    firewall.close();
}

void replace(string &str, string target, string substi){
    size_t pos = 0;
    while((pos = str.find(target, pos)) != string::npos){
        str.replace(pos, target.size(), substi);
        pos += substi.size();
    }
}

for rule 192.168.*.* the check_ruel should return true if ip like 192.168.231.67 and return false for IPs like 192.111.22.33