void free( void* ptr );
char * strdup( const char *str1 );

typedef struct WrenVM WrenVM;
const char* wrenGetSlotString(WrenVM* vm, int slot);
void wrenSetSlotString(WrenVM* vm, int slot, const char* text);

void C_strdup(WrenVM* vm) {
  const char *s = wrenGetSlotString(vm, 1);
  char *t = strdup(s);
  wrenSetSlotString(vm, 0, t);
  free(t);
}