learn_c_the_hard_way | 《learn c the hard way》Chinese translation | Translation library

A segmentation fault happens when the code try to access a memory region that is not available.

Accessing an array out of bounds doesn't means that the memory before or after the area occupied by the array is not available: The compiler or the runtime usually put all varibales or data in general in a given block of memory. If your array is the last item of such a memory block, the accessing it with a to big index will produce a Segmentaion Fault but is the array is in the middle of the memory block, you will just access memory used for other data, giving unexpected result and undefined behavior.

If the array (In may example, but valid for anything) is written, accessing available memory will not produce a segmentation fault but will overwrite something else. It may produce unexpected results or crash or segmentation fault later! This kind of bug is frequently very difficult to find because the unexpected result/behavior looks completely independent of the root cause.