updated for C++11
(important note for compiler regex support: for gcc. you need version 4.9 or later. i tested this on g++ version 4.9[1], and 9.2. cppreference.com has in browser compiler that i used.)
Thanks to user @2b-t who found a bug in the c++11 code!
Here is the C++11 code:
#include <iostream>
#include <string>
#include <regex>
using std::cout;
using std::endl;
int main() {
std::string input = "Example_45-3";
std::string output = std::regex_replace(
input,
std::regex("[^0-9]*([0-9]+).*"),
std::string("$1")
);
cout << input << endl;
cout << output << endl;
}
boost solution that only requires C++98
Minimal implementation example that works on many strings (not just strings of the form "text_45-text":
#include <iostream>
#include <string>
using namespace std;
#include <boost/regex.hpp>
int main() {
string input = "Example_45-3";
string output = boost::regex_replace(
input,
boost::regex("[^0-9]*([0-9]+).*"),
string("\\1")
);
cout << input << endl;
cout << output << endl;
}
console output:
Example_45-3
45
Other example strings that this would work on:
- "asdfasdf 45 sdfsdf"
- "X = 45, sdfsdf"
For this example I used g++ on Linux with #include <boost/regex.hpp> and -lboost_regex. You could also use C++11x regex.
Feel free to edit my solution if you have a better regex.
Commentary:
If there aren't performance constraints, using Regex is ideal for this sort of thing because you aren't reinventing the wheel (by writing a bunch of string parsing code which takes time to write/test-fully).
Additionally if/when your strings become more complex or have more varied patterns regex easily accommodates the complexity. (The question's example pattern is easy enough. But often times a more complex pattern would take 10-100+ lines of code when a one line regex would do the same.)
[1]
[1]
Apparently full support for C++11 <regex> was implemented and released for g++ version 4.9.x and on Jun 26, 2015. Hat tip to SO questions #1 and #2 for figuring out the compiler version needing to be 4.9.x.
