Exception header in C++ with examples
C++ provides a list of standard exceptions defined in header <exception> in namespace std where “exception” is the base class for all standard exceptions. All exceptions like bad_alloc, bad_cast, runtime_error, etc generated by the standard library inherit from std::exception. Therefore, all standard exceptions can be caught by reference.
Below are the errors are thrown in C++:
|bad_alloc||thrown by new on allocation failure|
|bad_cast||thrown by dynamic_cast when it fails in a dynamic cast|
|bad_exeption||thrown by certain dynamic exception specifiers|
|bad_typeid||thrown by typeid|
|bad_function_call||thrown by empty function objects|
|bad_weak_ptr||thrown by shared_ptr when passed a bad weak_ptr|
|logic_error||error related to the internal logic of the program|
|runtime_error||error related to the internal logic of the program|
Below is the program to illustrate some of the errors in exception class in C++:
Below is the illustration of std::bad_alloc error:
using class bad_alloc
using class exception
Array created successfully of length 1000 std::bad_alloc for array of length 1000000000
- For creating an array of length 1000 the memory allocation was successful and there was no exception thrown for the same.
- For creating an array of length 1000 the memory allocation was not successful and the exception “std::bad_alloc” was thrown. The exception thrown is of type bad_alloc which is derived from the class exception. The function what() is a virtual function defined in the base class exception. The function what() returns a null terminated string which is generally a description of error.
Why did we catch an exception by reference?
Catching an exception by value will call the copy constructor and create a copy of the exception which adds run-time overhead. Thus, catching by reference is a better option. If we want to modify exception or add some additional information to the error message then catching by reference is best for it. For this case:
The above program wants to catch the exception, add some information to it and re-throw it. But str is a call by value variable which gets changed locally in the function and when the function re-throw the exception then the original exception is passed.
Below is the program to illustrate the logic_error:
Factorial of 0 is 1 Factorial of 3 is 6 negative not allowed