Verisk OA 面试真题解析：C++ 虚析构与字符串转整数

C++ Virtual Destruction and String to Integer Conversion

1) Consider the following classes:

#include <memory>

struct Base {virtual void f();
};

struct Derived : Base {};

void f() {std::unique_ptr<Base> b = std::make_unique<Derived>();
}

void f() {Base* b = new Derived();
    // ...
    delete b;
}

int main() {f();
    return 0;
}

2) Implement a function to convert a string to a number.

// function to convert string to a number
// 32 signed integer with sign
int convert(std::string str) {
    int num = 0;
    return num;
}

int main() {
    // Given string of number
    char s[] = "-123";
    int str2num = convert(s);
    std::cout << "number -" << str2num << std::endl;
    return 0;
}

What is wrong with the first snippet, and how would you correctly implement the string-to-integer conversion in the second snippet?

这道题其实包含两个常见的 C++ 面试点：第一部分考察多态对象的析构行为，`Base*` 指向 `Derived` 时如果基类没有虚析构函数，直接 `delete b` 会导致派生类资源无法被正确释放；而 `std::unique_ptr<Base>` 配合虚析构则能安全管理基类指针指向派生对象。第二部分是字符串转整数，需要正确处理正负号、逐位累加、非法字符以及可能的溢出问题，常见做法是先判断符号位，再遍历字符并按十进制构造结果，必要时在边界处做 `INT_MAX/INT_MIN` 检查。