#include <iostream>

#include <string.h>

using namespace std;

extern char **environ;

void PrintValue(string value);

int main() {

     string name{"SILLY"};

     cout << endl;
     // the c++ compiler has trouble with casting a const char * to a char *
     // any of the three of these are fine.
     // See the notes.
#if defined(CASE1)
     string  sillyVar{"SILLY=Now I am"};
     cout << "\tusing string sillyvar " << endl;
#elif defined(CASE2)
     char* sillyVar = strdup("SILLY=Now I Am");
     cout << "\tUsing char* sillyVar" << endl;
#elif defined(CASE3)
     const char* sillyVar{"SILLY=Now I Am"};
     cout << "\tUsing const char* sillyVar" << endl;
#else
     char sillyVar[] = "SILLY=Now I Am";
     cout << "\tUsing char sillyVar[] " << endl;
#endif

     cout << endl;

     PrintValue("LOGNAME");
     PrintValue(name);


     cout << "The environ pointer is " << environ << endl;

#ifdef CASE1
     if (putenv(const_cast<char *>(sillyVar.c_str())) == -1) {
#else
   #ifdef CASE3
     if (putenv(const_cast<char *>(sillyVar)) == -1) {
   #else
     if (putenv(sillyVar) == -1) {
   #endif
#endif

         cerr << "Unable to change the SILLY environment variable" << endl;
     } else {

          PrintValue(name);
     }
     cout << "The environ pointer is " << environ << endl;

#ifdef CASE2
      free(sillyVar);
#endif
     return 0;
}

void PrintValue(string name) {
     char * tmp;

     cout << endl;
     cout << "Searching for " << name << endl;
     cout << "\t";

     tmp = getenv(name.c_str());
      
     if (tmp != nullptr) {
        cout << name << " is " << tmp << endl;
     } else {
        cout << name << " is not in the environment. "<< endl;
     }

     cout << endl;
     
     return;
}