#include <iostream>
#include <string>
using namespace std;
 
struct mystring : public std::string
{
    // ... appropriate constructors are an exercise left to the reader
    mystring& operator=(const char* right)
    {
        if (right == NULL)
            clear();
        else
            std::string::operator=(right);
        return *this;
    }
};
 
int main() {
	mystring s1, s2;
	s1 = NULL;
	s2 = "hello";
	cout << "-" << s1 << "- -" << s2 << "-" << endl;
	return 0;
}

I2luY2x1ZGUgPGlvc3RyZWFtPgojaW5jbHVkZSA8c3RyaW5nPgp1c2luZyBuYW1lc3BhY2Ugc3RkOwoKc3RydWN0IG15c3RyaW5nIDogcHVibGljIHN0ZDo6c3RyaW5nCnsKICAgIC8vIC4uLiBhcHByb3ByaWF0ZSBjb25zdHJ1Y3RvcnMgYXJlIGFuIGV4ZXJjaXNlIGxlZnQgdG8gdGhlIHJlYWRlcgogICAgbXlzdHJpbmcmIG9wZXJhdG9yPShjb25zdCBjaGFyKiByaWdodCkKICAgIHsKICAgICAgICBpZiAocmlnaHQgPT0gTlVMTCkKICAgICAgICAgICAgY2xlYXIoKTsKICAgICAgICBlbHNlCiAgICAgICAgICAgIHN0ZDo6c3RyaW5nOjpvcGVyYXRvcj0ocmlnaHQpOwogICAgICAgIHJldHVybiAqdGhpczsKICAgIH0KfTsKCmludCBtYWluKCkgewoJbXlzdHJpbmcgczEsIHMyOwoJczEgPSBOVUxMOwoJczIgPSAiaGVsbG8iOwoJY291dCA8PCAiLSIgPDwgczEgPDwgIi0gLSIgPDwgczIgPDwgIi0iIDw8IGVuZGw7CglyZXR1cm4gMDsKfQ==