In C++, Exception Handling is a process to handle runtime errors. Exception is an event which is thrown at runtime in C++. All exceptions are derived from std::exception class. It is a runtime error which can be handled. It prints exception message and terminates the program, if we don't handle the exception.
Exceptions are defined in C++ standard as <exception> class that we can use inside our programs. The arrangement of parent-child class hierarchy has been shown below:
Common exception classes in C++ are:
Exception | Description |
---|---|
std::exception | This is an exception and parent class of all the standard C++ exceptions. |
std::bad_cast | It is an exception thrown by dynamic_cast. |
std::bad_exception | This exception is used to handle the unexpected exceptions in a C++ program. |
std::bad_alloc | It is generally be thrown by new. |
std::logic_failure | This exception can be detected by reading a code. |
std::runtime_error | This exception cannot be detected by reading a code |
std::bad_typeid | It is an exception thrown by typeid. |
There are 3 keywords in exception handling: try, catch and throw.
In C++, exception handling is performed using try/catch statement. The code that may occur exception is used to place by Try block. Catch block is used to handle the exception.
#include <iostream> using namespace std; class Sample1 { public: Sample1() { cout << "Construct an Object of sample1" << endl; } ~Sample1() { cout << "Destruct an Object of sample1" << endl; } }; class Sample2 { public: Sample2() { int i=7; cout << "Construct an Object of sample2" << endl; throw i; } ~Sample2() { cout << "Destruct an Object of sample2" << endl; } }; int main() { try { Sample1 s1; Sample2 s2; } catch(int i) { cout << "Caught " << i << endl; } }
Construct an Object of sample1 Construct an Object of sample2 Destruct an Object of sample1 Caught 7
We can define our own exceptions by inheriting and overriding exception class functionalities.
#include <iostream> #include <exception> using namespace std; struct DivideByZero : public exception { const char * what () const throw () { return "My Exception"; } }; int main() { try { throw DivideByZero(); } catch(DivideByZero& e) { cout << "Exception caught" << endl; cout << e.what() << endl; } catch(exception& e) { } }
Exception caught My Exception what() = A public method provided by exception class and it has been overridden by all the child exception classes. It returns the cause of an exception.