If an exception is thrown in the constructor, will the destructor be called?

No, the destructor will not be called.

If an exception occurs during the execution of a class constructor, the object is considered not fully constructed. In such cases, C++ does not call the destructor for this partially constructed object. Destructors are only called for fully constructed sub-objects (base classes or class members).

Example:

#include <iostream>
#include <stdexcept>

class MyClass {
public:
    MyClass() {
        std::cout << "MyClass constructor" << std::endl;
        throw std::runtime_error("Constructor error");
    }

    ~MyClass() {
        std::cout << "MyClass destructor" << std::endl; // This code will not be executed
    }
};

int main() {
    try {
        MyClass obj; // Exception will be thrown here
    } catch (const std::runtime_error& e) {
        std::cerr << "Caught exception: " << e.what() << std::endl;
    }
    return 0;
}

Program output:

MyClass constructor
Caught exception: Constructor error

Destructor ~MyClass() is not called.