Editing Unreachable code (section)

==Causes==
Unreachable code can exist for many reasons, such as:
* programming errors in complex conditional branches
* a consequence of the internal transformations performed by an [[optimizing compiler]];
* incomplete testing of new or modified code
* Legacy code
** Code superseded by another implementation
** Unreachable code that a programmer decided not to delete because it is mingled with reachable code
** Potentially reachable code that current use cases never need
** Dormant code that is kept intentionally in case it is needed later
* Code used only for debugging.

Legacy code is that which was once useful but is no longer used or required. But unreachable code may also be part of a complex library, module or routine where it is useful to others or under conditions which are not met in a particular scenario.

An example of such a conditionally unreachable code may be the implementation of a general string formatting function in a compiler's runtime library, which contains complex code to process all possible arguments, of which only a small subset is actually used. Compilers will typically not be able to remove the unused code sections at compile time, as the behavior is largely determined by the values of arguments at run time.