C++ replace multiple strings in a string in a single pass

Question

Given the following string, "Hi ~+ and ^*. Is ^* still flying around ~+?"

I want to replace all occurrences of "~+" and "^*" with "Bobby" and "Danny", so the string becomes:

"Hi Bobby and Danny. Is Danny still flying around Bobby?"

I would prefer not to have to call Boost replace function twice to replace the occurrences of the two different values.

Answer 1

I managed to implement the required replacement function using Boost.Iostreams. Specifically, the method I used was a filtering stream using regular expression to match what to replace. I am not sure about the performance on gigabyte sized files. You will need to test it of course. Anyway, here's the code:

#include <boost/regex.hpp>
#include <boost/iostreams/filter/regex.hpp>
#include <boost/iostreams/filtering_stream.hpp>
#include <iostream>

int main()
{
   using namespace boost::iostreams;

   regex_filter filter1(boost::regex("~\\+"), "Bobby");
   regex_filter filter2(boost::regex("\\^\\*"), "Danny");

   filtering_ostream out;
   out.push(filter1);
   out.push(filter2);
   out.push(std::cout);

   out << "Hi ~+ and ^*. Is ^* still flying around ~+?" << std::endl;

   // for file conversion, use this line instead:
   //out << std::cin.rdbuf();
}

The above prints "Hi Bobby and Danny. Is Danny still flying around Bobby?" when run, just like expected.

It would be interesting to see the performance results, if you decide to measure it.

Daniel

Edit: I just realized that regex_filter needs to read the entire character sequence into memory, making it pretty useless for gigabyte-sized inputs. Oh well...