substrneg

substrneg.cpp

// substrneg.cpp
// juanfc 2024-11-11
// https://gist.github.com/juanfal/fe6f9f7369ff4358c80725781949a6ca

#include <iostream>
using namespace std;

int main()
{
  void tryThis(string s, int from, int end = -1);

  tryThis("abcdefgh", 2);      //  "cdefgh"
  tryThis("abcdefgh", -2);     //  "gh"
  tryThis("abcdefgh", -1);     //  "h"
  tryThis("abcdefgh", -3, -2); //  "fg"
  tryThis("abcdefgh", 4, 4);   //  "e"
  tryThis("abcdefgh", 4, -2);  //  "efg"
  tryThis("abcdefgh", 4, 3);   //  ""
  tryThis("abcdefgh", 40, 50); //  ""

  return 0;
}

string substrneg(string s, int from, int end = -1)
{
  string r;
  int    len = s.length();

  if (from < 0)
    from = len + from;
  if (end < 0)
    end = len + end;
  if (end > len - 1)
    end = len - 1;

  for (int i = from; i <= end; ++i)
    r += s[i];

  return r;
}

void tryThis(string s, int from, int to)
{
  string substrneg(string s, int from, int end = -1);
  cout << "substrneg(\"" << s << "\", " << from << ", " << to << "): \""
       << substrneg(s, from, to) << '"' << endl;
}