C++ Regular Expressions with Boost Regex - c++

Question

I am trying to take a string in C++ and find all IP addresses contained inside, and put them into a new vector string.
I've read a lot of documentation on regex, but I just can't seem to understand how to do this simple function.
I believe I can use this Perl expression to find any IP address:
re("\b(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\b");
But I am still stumped on how to do the rest.

Answer 1

Perhaps you're looking for something like this. It uses regex_iterator to get all matches of the current pattern. See reference.
#include <boost/regex.hpp>
#include <iostream>
#include <string>
int main()
{
std::string text(" 192.168.0.1 abc 10.0.0.255 10.5.1 1.2.3.4a 5.4.3.2 ");
const char* pattern =
"\\b(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)"
"\\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)"
"\\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)"
"\\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\b";
boost::regex ip_regex(pattern);
boost::sregex_iterator it(text.begin(), text.end(), ip_regex);
boost::sregex_iterator end;
for (; it != end; ++it) {
std::cout << it->str() << "\n";
// v.push_back(it->str()); or something similar
}
}
Output:
192.168.0.1
10.0.0.255
5.4.3.2
Side note: you probably meant \\b instead of \b; I doubt you watnted to match backspace character.

Answer 2

The offered solution is quite good, thanks for it. Though I found a slight mistake in the pattern itself.
For example, something like 49.000.00.01 would be taken as a valid IPv4 address and from my understanding, it shouldn't be (just happened to me during some dump processing).
I suggest to improve the patter into:
"\\b(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9][0-9]?|0)"
"\\.(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9][0-9]?|0)"
"\\.(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9][0-9]?|0)"
"\\.(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9][0-9]?|0)\\b";
This should allow only 0.0.0.0 as the all-zero-in, which I suppose to be correct and it will eliminate all .00. .000. etc.

Answer 3

#include <string>
#include <list>
#include <boost/regex.hpp>
typedef std::string::const_iterator ConstIt;
int main()
{
// input text, expected result, & proper address pattern
const std::string sInput
(
"192.168.0.1 10.0.0.255 abc 10.5.1.00"
" 1.2.3.4a 168.72.0 0.0.0.0 5.4.3.2"
);
const std::string asExpected[] =
{
"192.168.0.1",
"10.0.0.255",
"0.0.0.0",
"5.4.3.2"
};
boost::regex regexIPs
(
"(^|[ \t])("
"(2(5[0-5]|[0-4][0-9])|1[0-9][0-9]|[1-9]?[0-9])[.]"
"(2(5[0-5]|[0-4][0-9])|1[0-9][0-9]|[1-9]?[0-9])[.]"
"(2(5[0-5]|[0-4][0-9])|1[0-9][0-9]|[1-9]?[0-9])[.]"
"(2(5[0-5]|[0-4][0-9])|1[0-9][0-9]|[1-9]?[0-9])"
")($|[ \t])"
);
// parse, check results, and return error count
boost::smatch what;
std::list<std::string> ns;
ConstIt end = sInput.end();
for (ConstIt begin = sInput.begin();
boost::regex_search(begin, end, what, regexIPs);
begin = what[0].second)
{
ns.push_back(std::string(what[2].first, what[2].second));
}
// check results and return number of errors (zero)
int iErrors = 0;
int i = 0;
for (std::string & s : ns)
if (s != asExpected[i ++])
++ iErrors;
return iErrors;
}