String compare using regex

Question

I have a string say:

std::string s1 = "@Hello$World@";

I want to match it with another string but only certain characters:

std::string s2 = "_Hello_World_";

The strings must have same length and exactly match ignoring the _ characters which can be anything. In other words, I want to match the sequence of "Hello" and "World" at same indexes.

I could use a loop here ignoring those indexes but I want to know if I can do this with regex expressions?

In regex, a dot matches any character (except newlines), so your regex would have to look like .Hello.World.. — Siguza
– Siguza, Commented Oct 17, 2015 at 10:29

dspfnder · Accepted Answer · 2015-10-17 10:53:48Z

3

The '.' (dot) operator inside a regex pattern will act as a substitute for any char. Below you have 3 strings with different separators that are matched by the pat variable...

#include <iostream>
#include <regex>

using namespace std;

int main()
{
    regex pat(".Hello.World.");
    // regex pat(.Hello.World., regex_constants::icase); // for case insensitivity

    string str1 = "_Hello_World_";
    string str2 = "@Hello@World@";
    string str3 = "aHellobWorldc";

    bool match1 = regex_match(str1, pat);
    bool match2 = regex_match(str2, pat);
    bool match3 = regex_match(str3, pat);

    cout << (match1 ? "Matched" : "Not matched") << endl;
    cout << (match2 ? "Matched" : "Not matched") << endl;
    cout << (match3 ? "Matched" : "Not matched") << endl;


    //system("pause");
    return 0;
}

edited Oct 17, 2015 at 10:53

answered Oct 17, 2015 at 10:37

dspfnder

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Comments

sh03 · Accepted Answer · 2015-10-17 10:38:27Z

2

Yes, you can just use std::regex_match like so:

std::string string("@Hello$World@");
std::regex regex("^.Hello.World.$");
std::cout << std::boolalpha << std::regex_match(string, regex);

Live demo

The . (dots) in the regex mean "any character", ^ means "starting of the string" and $ means ending of the string.

edited Oct 17, 2015 at 10:38

answered Oct 17, 2015 at 10:30

sh03

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6 Comments

user963241 Over a year ago

Is it also possible to match any lower case character instead of just any character?

sh03 Over a year ago

@user963241 Yes, with classes. Please, if you have any other question, open a new question instead of asking them here. The reason for this is that Stack Overflow is optimized for single straight forward questions + related answers; questions and answers in comments may not even be indexed well by search engines.

user963241 Over a year ago

Thanks. I want know just one thing related to the answer: if it is really necessary to use ^ and $ in regex. I think it works without them as well.

sh03 Over a year ago

@user963241 Depends on whether you want to match .Hello.World. anywhere in a string or match only if the whole string matches .Hello.World..

user963241 Over a year ago

But it still doesn't work for anywhere

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