Handling Constructor Exceptions

When an exception is thrown in a constructor, it cannot be caught within the constructor body itself. Instead, you need to use a function try block to catch the exception. Here's an example:

1#include <iostream>
2#include <stdexcept>
3
4class MyClass {
5 public:
6  MyClass(int value) try : mValue{value} {
7    if (value < 0) {
8      throw std::invalid_argument{
9        "Negative value"};
10    }
11  } catch (const std::exception& e) {
12    std::cout << "Exception caught: "
13      << e.what() << "\n";
14    throw;  // Rethrow the exception
15  }
16
17 private:
18  int mValue;
19};
20
21int main() {
22  try {
23    MyClass obj{-5};
24  } catch (const std::exception& e) {
25    std::cout << "Exception caught in main: "
26      << e.what() << "\n";
27  }
28}

1Exception caught: Negative value
2Exception caught in main: Negative value

In this example, the constructor of MyClass uses a function try block to catch any exceptions thrown during the initialization of mValue. If an exception is caught, it is printed and then rethrown.

The exception is then caught in the main() function, where it can be handled appropriately.

Remember, when an exception is caught in a constructor's function try block, it must be rethrown or replaced with another exception. It cannot be fully handled within the catch block itself.