C++ Programming/Exception Handling. Exception Handling[edit] Exception handling is a construct designed to handle the occurrence of exceptions, that is special conditions that changes the normal flow of program execution. Since when designing a programming task (a class or even a function), one cannot always assume that application/task will run or be completed correctly (exit with the result it was intended to). It may be the case that it will be just inappropriate for that given task to report an error message (return an error code) or just exit. To handle these types of cases, C++ supports the use of language constructs to separate error handling and reporting code from ordinary code, that is, constructs that can deal with these exceptions (errors and abnormalities) and so we call this global approach that adds uniformity to program design the exception handling.
An exception is said to be thrown at the place where some error or abnormal condition is detected. Stack unwinding[edit] Consider the following code Guards[edit] C++ Exception Handling. By Illco of Mayday Software Productions. Table of contents: Introduction This document is intended for those in need of a transparent and nice way to handle program errors. The text will introduce a widely used method for achieving this: exception handling. The described system is available in many programming language such as Java, C++, Modula-3, etc., but here we will focus on C++ exception handling.
There are several good reasons to use exception handling. How it was done before Before a system of exception handling was introduced, computer programs were certainly not error-free. In older systems every (interesting) function you would call would return a value indicating how well the execution went. If you have ever written a Windows application using the Windows API you have worked with this method. The concept of exception handling The global concept of exception handling is simple. Program Flow The raising of the imaginary error flag is simply called raising or throwing an error.
Understanding C++ Exception Handling. Introduction Exceptions have been around in C++ for a while and are pretty common. If you use the STL or even just new you have been exposed to exceptions. Of course, like all things in C++, having a language feature does not necessarily clearly point one in the direction of the best use of that feature. I would not dare to call myself an expert or authority on exception handling, but as a user of C++ I've had some exposure to using exceptions. This article will offer some insight into the use and potential misuse of exceptions. I highly recommend reading Scott Meyer's More Effective C++; there is a whole section devoted to exceptions.
I also use a few terms from John Lakos's Large Scale C++ Software Design. Overview of C++ Exception Handling C++ Exception Handling is centered around the three keywords: try, catch, and throw, the general purpose of which is to attempt to execute code and handle unexpected exceptional conditions, hence the name. Try { if ( ! Exception Specifications. C++ Exceptions. C++ Exceptions There's an exception to every rule. What Are Exceptions? In these Web pages we typically handle error conditions by detecting them with some sort of if test and then taking appropriate action when the condition is true.
Often the action is to print an error message and exit the program. An alternate way to handle error conditions is to "throw" an exception when some error condition becomes true. One then "tries" any code that might cause such an exception, "catching" any exception that was raised, and taking appropriate action when an exception is caught. A Simple Example Take a look through the code for the above program. If the variable Num becomes too big we get out of the loop by throwing an exception. So, what happens when the exception is thrown? The main function uses the "try" construct to enclose the call of the PrintSequence function. You can also catch various types of exceptions separately. Exceptions in an Array-Based Stack Exceptions in a List-Based Stack Stacks.
Exception Handling in C. One benefit of C++ over C is its exception handling system. An exception is a situation in which a program has an unexpected circumstance that the section of code containing the problem is not explicitly designed to handle. In C++, exception handling is useful because it makes it easy to separate the error handling code from the code written to handle the chores of the program. Doing so makes reading and writing the code easier. Furthermore, exception handling in C++ propagates the exceptions up the stack; therefore, if there are several functions called, but only one function that needs to reliably deal with errors, the method C++ uses to handle exceptions means that it can easily handle those exceptions without any code in the intermediate functions. One consequence is that functions don't need to return error codes, freeing their return values for program logic. When errors occur, the function generating the error can 'throw' an exception.
C++ Exceptions: Pros and Cons. 1. Introduction Exceptions have been a part of C++ since early 1990s and are sanctioned by the standard to be the mechanism for writing fault-tolerant code in this language. However, many developers for various reasons choose not to use exceptions, and voices that are skeptical of this language feature are still numerous and loud: Raymond Chen's article Cleaner, more elegant, and wrong, Joel Spolsky's blog Exceptions, and Google C++ Style Guide are some of the frequently quoted texts that advise against the use of exceptions. Rather than taking a side in this debate, I am trying to present a balanced view of pros and cons of using exceptions. 2. 2.1 Exceptions separate error-handling code from the normal program flow and thus make the code more readable, robust, and extensible. To illustrate the point, we'll compare the usage of two simple socket libraries that differ only in the error handling mechanism.
Now, consider a version that uses error codes: What about robustness? 3. Exceptions. Exceptions provide a way to react to exceptional circumstances (like runtime errors) in programs by transferring control to special functions called handlers. To catch exceptions, a portion of code is placed under exception inspection. This is done by enclosing that portion of code in a try-block. When an exceptional circumstance arises within that block, an exception is thrown that transfers the control to the exception handler. If no exception is thrown, the code continues normally and all handlers are ignored. An exception is thrown by using the throw keyword from inside the try block. Exception handlers are declared with the keyword catch, which must be placed immediately after the try block: The code under exception handling is enclosed in a try block.
A throw expression accepts one parameter (in this case the integer value 20), which is passed as an argument to the exception handler. It is also possible to nest try-catch blocks within more external try blocks. Exception specification. Exception. Class Standard exception class Base class for standard exceptions. All objects thrown by components of the standard library are derived from this class. Therefore, all standard exceptions can be caught by catching this type by reference. It is declared as: Member functions (constructor) Construct exception ( public member function ) operator= Copy exception ( public member function ) what (virtual) Get string identifying exception ( public member function ) (destructor) (virtual) Destroy exception ( public virtual member function ) Derived types (scattered throughout different library headers) bad_alloc Exception thrown on failure allocating memory (class ) bad_cast Exception thrown on failure to dynamic cast (class ) bad_exception Exception thrown by unexpected handler (class ) bad_function_call Exception thrown on bad call (class ) bad_typeid Exception thrown on typeid of null pointer (class ) bad_weak_ptr Bad weak pointer (class ) ios_base::failure Base class for stream exceptions (public member class ) Example.
[17] Exceptions and error handling Updated! C++ Exception Handling.