strtok and replace a substring in C++

If I have a string "12 23 34 56"

What's the easiest way to change it to "\x12 \x23 \x34 \x56"?

From stackoverflow

• string s = "12 23 34 45";
  stringstream str(s), out;
  int val;
  while(str >> val)
      out << "\\x" << val << " "; // note: this puts an extra space at the very end also
                                 //       you could hack that away if you want
  
  // here's your new string
  string modified = out.str();
  

  Evan Teran : it avoid the extra space, just prepend a "\x" before you start and change the line in the while to be: out << " \x" << val;

  Evan Teran : though from his comments, it looks like he wants a string with chars 0x12, 0x34, 0x56, 0x78 not a string containing "\x12 \x34 \x56 \x78".

  Martin York : You mean "\\x"

  Jesse Beder : Whoops, I just noticed that; thanks for the edit, Evan.

• You can do this like so:

  foreach( character in source string)
  {
    if 
      character is ' ', write ' \x' to destination string
    else 
      write character to destination string.
  }
  

  I suggest using std::string but this can be done easily by first checking the string to count how many whitespaces and then create your new destination string to be that number x3.

• You question is ambiguous, it depends on what you actually want:

  if you want the result be the same as: char s[] = { 0x12, 0x34, 0x56, 0x78, '\0'}: then you could do this:

  std::string s;
  int val;
  std::stringstream ss("12 34 56 78");
  while(ss >> std::hex >> val) {
     s += static_cast<char>(val);
  }
  

  after this, you can test it with this:

  for(int i = 0; i < s.length(); ++i) {
      printf("%02x\n", s[i] & 0xff);
  }
  

  which will print:

  12
  34
  56
  78
  

  otherwise if you want your string to literally be "\x12 \x23 \x34 \x56" then you could do what Jesse Beder suggested.