CODEWITHSUNDEEP
c++boost
Rafał Franczyk
Rafał Franczyk

Reputation: 11

boost regex to find digits

I need to validate input, only 2 or 3 digits should be allowed.

I am not sure why boost::regex_match is returning true for 4 digits scenario ?

boost::smatch base_match;
boost::regex base_regex("[0-9]{2,3}");
std::string same_digits("1234"));
if (boost::regex_match(same_digits, base_match, base_regex)) 
{
   std::cout << " It is True!"<< std::endl;
}

How to write boost regex to get result like ^[0-9]{2,3}$

Upvotes: 1

Views: 332

Answers (1)

sehe
sehe

Reputation: 393114

I'm also not sure. This is what I see:

Live On Coliru

#include <boost/regex.hpp>
#include <iostream>
#include <iomanip>

int main() {
    boost::smatch m;
    boost::regex  r("[0-9]{2,3}");

    for (std::string const input :
         {"", "1", "12", "123", "1234", "12345"}) //
    {
        std::cout << std::quoted(input) << " -> " << std::boolalpha
                  << regex_match(input, m, r)
                  << std::endl;
    }
}

Prints

"" -> false
"1" -> false
"12" -> true
"123" -> true
"1234" -> false
"12345" -> false

Note that this is different from regex_search. You need the ^$ anchors there: Compare http://coliru.stacked-crooked.com/a/a89fe8931d04ad99 to http://coliru.stacked-crooked.com/a/a430319477fa3b52

Upvotes: 1

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