C++自定义ZeroCheck异常输出格式不符合预期的问题求助

Let's break down what's going wrong here and fix it step by step!

The Root Cause #

Your issue stems from how the operator<< is structured: when you output Math3, the operator first prints "Quotient is: " to the stream, then calls division()—which throws the ZeroCheck exception. By the time the exception is caught, the "Quotient is: " text is already in the output and can't be undone, leading to the messy combined message. Additionally, your ZeroCheck class's what() method doesn't follow C++ exception best practices (it's not a const member function), which can cause subtle issues.

Fixes to Implement #

1. Update the ZeroCheck Exception Class

Align it with standard C++ exception conventions by making what() a const member function, and use initializer lists for cleaner construction:

// ZeroCheck.h
#ifndef ZEROCHECK_H_INCLUDED
#define ZEROCHECK_H_INCLUDED
#include <string>
using std::string;

class ZeroCheck {
public:
    ZeroCheck() : msg("") {}
    ZeroCheck(const string& _msg) : msg(_msg) {}
    
    // Make what() const and return a const reference for efficiency
    const string& what() const { 
        return msg; 
    }
private:
    string msg;
};
#endif /* ZEROCHECK_H_INCLUDED */

2. Rewrite the operator<< to Handle Exceptions Before Outputting the Quotient Label

We'll adjust the logic to first attempt calculating the quotient, then decide what to print—this way, we never output "Quotient is: " if division fails:

// In main.cpp, replace your existing operator<< with this
template<class T>
ostream& operator<<(ostream& os, Mathematics<T>& obj) {
    os << "The result of calculation for: " << obj.val1 << " and " << obj.val2 << '\n'
       << "Sum is: " << obj.addition() << '\n'
       << "Difference is: " << obj.subtraction() << '\n'
       << "Product is: " << obj.multiplication() << '\n';
    
    // Handle division separately to avoid premature label output
    try {
        T quotient = obj.division();
        os << "Quotient is: " << quotient << '\n';
    } catch (const ZeroCheck& e) {
        // Print only the error message when division fails
        os << e.what() << '\n';
    }
    
    return os;
}

3. Fix the Minor Typo in main()

Your expected output has Math 3: (with a colon), but your code prints Math 3 without it. Correct that line:

// In main.cpp
cout << "Math 3:" << '\n'; // Add the missing colon

Optional Alternative: Handle Exceptions in main() Instead #

If you prefer to keep exception handling centralized in main() instead of the output operator, you can split the output of Math3 into separate parts (you'll need to make val1/val2 public or add getter methods to Mathematics):

int main() {
 try {
     Mathematics<int> Math1(10, 5);
     Mathematics<double> Math2(5.5, 3.4);
     Mathematics<int> Math3(6, 0);
     
     cout << "Math 1:" << '\n';
     cout << Math1 << '\n' << '\n';
     
     cout << "Math 2:" << '\n';
     cout << Math2 << '\n';
     
     cout << "Math 3:" << '\n';
     // Print non-division results first
     cout << "The result of calculation for: " << Math3.val1 << " and " << Math3.val2 << '\n'
          << "Sum is: " << Math3.addition() << '\n'
          << "Difference is: " << Math3.subtraction() << '\n'
          << "Product is: " << Math3.multiplication() << '\n';
     // Attempt division separately so exceptions are caught in main()
     int quotient = Math3.division();
     cout << "Quotient is: " << quotient << '\n';
 } catch (const ZeroCheck& e) {
     cerr << e.what() << '\n';
 }
 return EXIT_SUCCESS;
}

Final Result #

After applying these changes, your output will match exactly what you expected:

Math 1:
The result of calculation for: 10 and 5
Sum is: 15
Difference is: 5
Product is: 50
Quotient is: 2

Math 2:
The result of calculation for: 5.5 and 3.4
Sum is: 8.9
Difference is: 2.1
Product is: 18.7
Quotient is: 1.61765

Math 3:
The result of calculation for: 6 and 0
Sum is: 6
Difference is: 6
Product is: 0
Denominator is 0, invalid division.

内容的提问来源于stack exchange，提问作者jr.çhåvez__07