在C++中，如何使用std::stringstream来转换一个整数为字符串？

A.

int num = 42;

std::stringstream ss;

ss << num;

ss.str();

B.

int num = 42;

std::stringstream ss;str(num);

ss.str();

C.

int num = 42;

std::stringstream ss;stream(num);

ss.str();

D.

int num = 42;

std::stringstream ss;

ss << "num is " << num;

ss.str();