Writing Custom Exception Class In C++
Follow the series “C++ By Examples” for all the C++ tutorials.
Exceptions is a way to handle run time errors arise during the execution of program. There are multiple types of exceptions. That includes bad_alloc, bad_cast, bad_typeid, logic_error, domain_error, invalid_argument, out_of_range, runtime_error, range_error, overflow_error, underflow_error and bad_exception. I listed all exceptions here on purpose. Because to find exception types again, you don’t need to wade through c++ source! And for enthusiasts, these exception types are defined in /usr/include/c++/4.4/bits/functexcept.h file. Let’s get back to the topic. I assume, basic usage of exceptions known to you. In this article I’ll show example on how-to write your own exception class which derives from the standard exception class ( Source at /usr/include/c++/4.4/exception).
Our custom Exception class will derive from the std::exception class and override what() method. There is one demo class of which method f() throws our custom Exception. We put that code in try-catch block to handle the custom exception thrown.
Below is the file 005_use_exception.cpp which houses all the action… Makefile can be used from this article.
/**
* File Name : 005_use_exception.cpp
* Functionality : Overriding the standard exception class to make your
own Exception class
* Copyright (C) 2012 Divyang Patel
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <iostream>
#include <exception>
using namespace std;
class Exception : public exception
{
public:
Exception(const char* errMessage):errMessage_(errMessage){}
// overriden what() method from exception class
const char* what() const throw() { return errMessage_; }
private:
const char* errMessage_;
};
class DemoEx
{
public:
DemoEx() throw(Exception&);
void f() throw(Exception&);
};
DemoEx::DemoEx() throw(Exception&)
{
try
{
f();
}
catch(Exception& e)
{
cout << "Caught Exception in ctor of DemoEx" << endl;
cout << e.what() << endl;
}
}
void DemoEx::f() throw(Exception&)
{
throw Exception("Exception explanation string called from e.what()");
}
int main()
{
DemoEx dobj;
return 0;
}
The output is as follows
Caught Exception in ctor of DemoEx Exception explanation string called from e.what()
Any doubts? Post in comments..
