Segmentation Fault

什么是“Segmentation Fault”
解释1：
One of the most common problems when making software is errors like "Segmentation fault", also called SegFault. Here is what a SegFault is. Virtual memory in a computer can be created in 2 ways: pages or segments. Paging means that the memory is divided in pages of equal size, containing words of memory in it. Segmentation means that every process has a segment of memory of needed size, with gaps of empty memory blocks between the segments. The operating system knows the upper limit of every segment, and every segment begins at a virtual address 0. When a program accesses a memory block, it calls a virtual address that the Memory Management Unit (MMU) maps to a real address. If the operating system sees that the requested address doesn't match any valid address in the segment, it will send a signal to the process terminating it. SegFaults are the direct result of a memory error. The program has a bad pointer, a memory leak or any kind of error that makes it access the wrong memory address. To correct these errors you need to check pointers and arrays for errors.

解释2：
An error in which a running program attempts to access memory not allocated to it and core dumps (A copy of the contents of core, produced when a process is aborted by certain kinds of internal error)with a segmentation violation error. This is often caused by improper usage of pointers in the source code, dereferencing a null pointer, or (in C) inadvertently using a non-pointer variable as a pointer.
The classic example is:

   int i;
   scanf ("%d", i);  /* should have used &i */