Convert string with explicit escape sequence into relative character

Question

I need a function to convert "explicit" escape sequences into the relative non-printable character. Es:

char str[] = "\\n";
cout << "Line1" << convert_esc(str) << "Line2" << endl:

would give this output:

Line1

Line2

Is there any function that does this?

Answer 1

You can do that fairly easy, using the boost string algorithm library. For example:

#include <string>
#include <iostream>
#include <boost/algorithm/string.hpp>

void escape(std::string& str)
{
  boost::replace_all(str, "\\\\", "\\");
  boost::replace_all(str, "\\t",  "\t");
  boost::replace_all(str, "\\n",  "\n");
  // ... add others here ...
}

int main()
{
  std::string str = "This\\tis\\n \\\\a test\\n123";

  std::cout << str << std::endl << std::endl;
  escape(str);
  std::cout << str << std::endl;

  return 0;
}

This is surely not the most efficient way to do this (because it iterates the string multiple times), but it is compact and easy to understand.

Update: As ybungalobill has pointed out, this implementation will be wrong, whenever a replacement string produces a character sequence, that a later replacement is searching for or when a replacement removes/modifies a character sequence, that should have been replaced.

An example for the first case is "\\\\n" -> "\\n" -> "\n". When you put the "\\\\" -> "\\" replacement last (which seems to be the solution at a first glance), you get an example for the latter case "\\\\n" -> "\\\n". Obviously there is no simple solution to this problem, which makes this technique only feasible for very simple escape sequences.

If you need a generic (and more efficient) solution, you should implement a state machine that iterates the string, as proposed by davka.