debugging - Why do I get: double free or corruption (top) after running this c++ script?

I've got the following piece of code:

Class Chain

with

char* c; 

as its only public atrib

istream& operator>>(istream& i, Chain& s) {
  delete [] s.c;
  const int L = 256;
  char *t = new char[L];
  i.getline(t,L);
  s.c = t;
  return i;

}

ostream& operator<<(ostream& o, Chain s) {
  o << s.c;
  return o;
}

#include 
#include "Chain.h"
using namespace std;


int main(){

      Chain id;

      cin >> id;

      cout << id;
      cout << id;

After running the code under the Eclipse IDE on Xubuntu (last version) I get the following error:

Error in [...] double free or corruption (top): 0x00000000008fd290 ***

What could be wrong?