C++11 trying to extract a substring using regex - c++

Question

This is my application:
// regex_example.cpp:
// How to compile:
// $ g++ -std=c++11 regex_example.cpp -o regex_example
#include <iostream>
#include <string>
#include <regex>
int main()
{
std::string input = "Pizza Carrot Lasagna 15000 ";
std::smatch match;
std::regex test_reg("[^0-9]*([0-9]+).*");
if (std::regex_search(input.begin(), input.end(), match, test_reg))
{
std::cout << "This is the string found: " << match[1] << std::endl;
}
return 0;
}
When I compile it, this is what the compiler shows me:
regex_example.cpp: In function ‘int main()’: regex_example.cpp:24:68:
error: no matching function for call to
‘regex_search(std::__cxx11::basic_string::iterator,
std::__cxx11::basic_string::iterator, std::__cxx11::smatch&,
std::__cxx11::regex&)’ if (std::regex_search(input.begin(),
input.end(), match, test_reg))
Basically, I'm trying to do the following:
1 - Have this compile. I don't understand why I'm getting the syntax error.
2 - From the input string, I'm trying to extract the number 15000. I'm assuming that when I get this compiling, I will get a string of 15000.

Answer 1

Using
std::regex_search(input.begin(), input.end(), match, test_reg)
Calls the overload
template< class BidirIt, class Alloc, class CharT, class Traits >
bool regex_search( BidirIt first, BidirIt last,
std::match_results<BidirIt,Alloc>& m,
const std::basic_regex<CharT,Traits>& e,
std::regex_constants::match_flag_type flags =
std::regex_constants::match_default );
and it requires that the match_result to be a std::match_results<BidirIt,Alloc>. In this case that is a std::string::iterator but match, which is a std::smatch, uses a std::string::const_iterator. Since those do not match, the compiler is unable to determine what BidirIt should deduce to.
There are many ways you can work around this but the simplest solution is to just use the std::string overload like:
std::regex_search(input, match, test_reg)
(Live Example)