Handling exceptions

• Use assertions to detect problems
• Use validation to detect and correct problems
• Use exceptions to detect and correct problems
• Create custom exceptions
• Throw exceptions

• #include <cassert>
• Do NOT use to validate user input
• Assertions are intended for detecting internal application errors that should not happen
• Assertions cause programs to terminate with an error message
• The error message generally includes the expression that failed, along with the filename and line number in the source code of the assertion
• Example: assert (divisor != 0);
• Example: assert (obj != NULL);

• Errors can be avoided by doing data validation
• Validation gets cumbersome in many circumstances
• It is difficult to write validation tests for all possibilities
• Validation is best used to check user input

• Exceptions are useful for catching any errors in a block of code
• The try block contains the code with potential errors
• The catch blocks contain code to be run when particular errors occur
• Example: try { // statements with possible exceptions } catch (datatype1 identifier1) { // statements run if a datatype1 exception is encountered above } catch (datatype2 identifier2) { // statements run if a datatype2 exception is encountered above } catch (...) { // statements run if exception other than those listed is encountered }
• Only the first matching catch block will be run when an exception is encountered
• You can throw an exception with any data type
• You can create your own classes for exceptions
• It is common to add a string object message to an exception class
• Include a getMessage() function to an exception class with a message
• Include a constructor that accepts a message argument when creating an exception class that includes a message
• Example of throwing an exception: throw 5;
• Example of throwing an exception: throw divisionByZero();
• You can rethrow an exception within a catch block using: throw;
• C++ base exception class is: exception
• Exceptions in C++ are divided into logic_error and runtime_error exceptions
• Logic_error exceptions include things such as invalid_argument and out_of_range
• Runtime_error exceptions include overflow_error and underflow_error