c++类处理异常的正确做法

#include <iostream>
#include <fstream>
#include <vector>
#include <cassert>
/*
    建议: 在类的构造函数中抛出异常 
 */
class A {
    public:
        A() {}
};
class B : public A {
    public:
        B() {}
        ~B() { /*std::cout << "byebye B\n";*/ }
    private:
        std::string m_value;
};
class GoodB : public B {
    public:
        GoodB() : m_v(new char(10000000)) {}
        GoodB(const char* f) : m_file(f, std::ios_base::in) {
            //在构造器里进行抛出异常,而不是一直判断是否有错误来避免错误.
            if(!m_file.is_open()) throw std::string("Couldn't open file..\n");

            std::string line;   
            while(std::getline(m_file, line)) {
                m_info.push_back(line);
            }
        }
        void doIt( GoodB const&b) {
            if(b.isOpen()) {
                //do    
            }
        }
        //通过析构来提示.
        ~GoodB() { assert((!isOpen()) && "open file: "); }
    private:
        char *m_v;
        std::fstream m_file; //外部文件 
        std::vector<std::string> m_info;
        //若作为状态判断,一般声明为私有函数, 通过assert来提示.
        bool isOpen() const { return !m_info.empty(); }
};
//循环构造, 内存崩溃
//想实现一个 std::out_of_memory 异常
void test() {
    int i = 0;
    for(;;) {
        try {
            ++i;    
            if(i % 10000 == 0) std::cout << "count i: " << i << std::endl;
            GoodB b;    
        } catch(...) {
            return ;    
        }
    }
}

void test2(char *filename) {
    try {
//在构造时候进行抛出异常,重复抛出, 不会出现问题, 而在析构函数中抛出,程序则会崩溃
        GoodB b(filename);  
        GoodB d(filename);
        b.doIt(b);
        //std::swap(b, d) //也不要抛出异常
    } catch(std::string msg) {
        std::cout << msg;
    }
}
int main(int argc, char** argv) {
    if(argc <= 1) return 1;
//  test();
    test2(argv[1]);
    std::cout << "exit!!!\n";
    return 0;
}