您不能将临时流投射到 std :: ostringstream& 。它格式错误（编译器必须告诉您它是错误的）。不过，可以执行以下操作：

You cannot cast the temporary stream to std::ostringstream&. It is ill-formed (the compiler must tell you that it is wrong). The following can do it, though:

f(static_cast<std::ostringstream&>(
  std::ostringstream().seekp(0) << "Value: " << 5).str().c_str());

那当然是丑陋的。但它显示了它如何工作。 seekp 是一个返回 std :: ostream& 的成员函数。一般情况下，***写上这样的

That of course is ugly. But it shows how it can work. seekp is a member function returning a std::ostream&. Would probably better to write this generally

template<typename T>
struct lval { T t; T &getlval() { return t; } };

f(static_cast<std::ostringstream&>(
  lval<std::ostringstream>().getlval() << "Value: " << 5).str().c_str());

没有任何东西就需要 void * $ c $的原因c>，是因为 operator<< 是成员函数。带有 char const * 的 operator 不是。

The reason that without anything it takes the void*, is because that operator<< is a member-function. The operator<< that takes a char const* is not.