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

I think that you must write such function yourself since escape characters is a compile-time feature, i.e. when you write "\n" the compiler would replace the \n sequence with the eol character. The resulting string is of length 1 (excluding the terminating zero character).

In your case a string "\\n" is of length 2 (again excluding terminating zero) and contains \ and n.

You need to scan your string and when encountering \ check the following char. if it is one of the legal escapes, you should replace both of them with the corresponding character, otherwise skip or leave them both as is.

( http://ideone.com/BvcDE ):

string unescape(const string& s)
{
  string res;
  string::const_iterator it = s.begin();
  while (it != s.end())
  {
    char c = *it++;
    if (c == '\\' && it != s.end())
    {
      switch (*it++) {
      case '\\': c = '\\'; break;
      case 'n': c = '\n'; break;
      case 't': c = '\t'; break;
      // all other escapes
      default: 
        // invalid escape sequence - skip it. alternatively you can copy it as is, throw an exception...
        continue;
      }
    }
    res += c;
  }

  return res;
}