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Common exceptions include an invalid argument (e.g. value is outside of the domain of a function), [5] an unavailable resource (like a missing file, [6] a network drive error, [7] or out-of-memory errors [8]), or that the routine has detected a normal condition that requires special handling, e.g., attention, end of file. [9]
Exception swallowing can also happen if the exception is handled and rethrown as a different exception, discarding the original exception and all its context. In this C# example, all exceptions are caught regardless of type, and a new generic exception is thrown, keeping only the message of the original exception.
C does not provide direct support to exception handling: it is the programmer's responsibility to prevent errors in the first place and test return values from the functions. In any case, a possible way to implement exception handling in standard C is to use setjmp/longjmp functions:
The implementation of exception handling in programming languages typically involves a fair amount of support from both a code generator and the runtime system accompanying a compiler. (It was the addition of exception handling to C++ that ended the useful lifetime of the original C++ compiler, Cfront. [18]) Two schemes are most common.
In a language that supports formal exception handling, a graceful exit may be the final step in the handling of an exception. In other languages graceful exits can be implemented with additional statements at the locations of possible errors.
Microsoft supports SEH as a programming technique at the compiler level only. MS Visual C++ compiler features three non-standard keywords: __try, __except and __finally — for this purpose. Other exception handling aspects are backed by a number of Win32 API functions, [2] for example, RaiseException to raise SEH exceptions manually.
Processor exceptions generated by the CPU have fixed mapping to the first up to 32 interrupt vectors. [1] While 32 vectors (0x00-0x1f) are officially reserved (and many of them are used in newer processors), the original 8086 used only the first five (0-4) interrupt vectors and the IBM PC IDT layout did not respect the reserved range.
A key mechanism for exception safety is a finally clause, or similar exception handling syntax, which ensure that certain code is always run when a block is exited, including by exceptions. Several languages have constructs that simplify this, notably using the dispose pattern , named as using , with , or try -with-resources.