请修改倒数第3行为： catch(A &){，原程序如下：#include <iostream> #include <exception> using namespace std; class A { }; int func1(int m, int n) { try { if (n == 0) throw A(); cout << "in func1" << endl; return m / n; } catch (exception) { cout << "catched in func1" << endl; } cout << "before end of func1" << endl; return m / n; } int main() { try { func1(5, 0); cout << "in main" << endl; } catch (A &a) { cout << "catched in main" << endl; } catch (A &) { cout << "end of main" << endl; } return 0; } ​

修改后的代码如下所示：

#include <iostream>
#include <exception>

using namespace std;

class A {};

int func1(int m, int n) {
    try {
        if (n == 0)
            throw A();
        cout << "in func1" << endl;
        return m / n;
    }
    catch (exception) {
        cout << "catched in func1" << endl;
    }
    cout << "before end of func1" << endl;
    return m / n;
}

int main() {
    try {
        func1(5, 0);
        cout << "in main" << endl;
    }
    catch (A &a) {
        cout << "catched in main" << endl;
    }
    catch (A &) {
        cout << "end of main" << endl;
    }
    return 0;
}

在修改后的代码中，将 `catch (A &)` 修改为 `catch (A &a)`。这是因为在 `catch (A &)` 后面没有指定变量名，而在 `catch (A &a)` 中，我们指定了变量名为 `a`。这样做的好处是，在 `catch (A &a)` 的代码中，我们可以使用变量 `a` 来处理捕获到的异常，而不需要使用默认的匿名变量。