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. |
Keywords:
There are 3 keywords in exception handling: try, catch and throw.
Try/Catch block:
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.
Example Code
#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;
}
}Output
Construct an Object of sample1 Construct an Object of sample2 Destruct an Object of sample1 Caught 7
User Defined Exception:
We can define our own exceptions by inheriting and overriding exception class functionalities.
Example Code
#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) {
}
}Output
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.