运行下面的代码，将出现（ ）。
1 double hmean(double a, double b) {
2 if (a == -b )
3 throw runtime_error("Runtime error occurred.");
4 return 2.0*a*b/(a + b);
5 }
6
7 int main() {
8 double x = 10;
9 double y = -10;
10
11 try {
12 int result = hmean(x, y);
13 cout << "hmean: " << result << endl;
14 }
15 catch (const runtime_error& e) {
16 cout << "Caught: " << e.what() << endl;
17 } catch (...) {
18 cout << "Caught an unknown exception." << endl;
19 }
20 return 0;
21 }
屏幕上输出Caught:Runtime error occurred.
屏幕上输出Caught an unknown exception.
程序调用std::terminate()
编译错误