在测试代码时，您可能想尝试使用Valgrind中的memcheck工具——它不会捕获堆栈框架内的单个数组边界违规，但它应该捕获许多其他类型的内存问题，包括那些会导致单个函数范围之外的微妙、更广泛的问题的问题。

摘自手册:

Memcheck is a memory error detector. It can detect the following problems that are common in C and C++ programs. Accessing memory you shouldn't, e.g. overrunning and underrunning heap blocks, overrunning the top of the stack, and accessing memory after it has been freed. Using undefined values, i.e. values that have not been initialised, or that have been derived from other undefined values. Incorrect freeing of heap memory, such as double-freeing heap blocks, or mismatched use of malloc/new/new[] versus free/delete/delete[] Overlapping src and dst pointers in memcpy and related functions. Memory leaks.

ETA:不过，正如卡兹的回答所说，它不是万能的，并且并不总是提供最有帮助的输出，特别是当您使用令人兴奋的访问模式时。

一般来说，现在的操作系统(流行的操作系统)使用虚拟内存管理器在受保护的内存区域中运行所有应用程序。事实证明，简单地读取或写入存在于已分配给进程的区域之外的REAL空间中的位置(就其本身而言)并不容易。

直接回答:

Reading will almost never directly damage another process, however it can indirectly damage a process if you happen to read a KEY value used to encrypt, decrypt, or validate a program / process. Reading out of bounds can have somewhat adverse / unexpected affects on your code if you are making decisions based on the data you are reading The only way your could really DAMAGE something by writing to a loaction accessible by a memory address is if that memory address that you are writing to is actually a hardware register (a location that actually is not for data storage but for controlling some piece of hardware) not a RAM location. In all fact, you still wont normally damage something unless you are writing some one time programmable location that is not re-writable (or something of that nature). Generally running from within the debugger runs the code in debug mode. Running in debug mode does TEND to (but not always) stop your code faster when you have done something considered out of practice or downright illegal. Never use macros, use data structures that already have array index bounds checking built in, etc....

ADDITIONAL I should add that the above information is really only for systems using an operating system with memory protection windows. If writing code for an embedded system or even a system utilizing an operating system (real-time or other) that does not have memory protection windows (or virtual addressed windows) that one should practice a lot more caution in reading and writing to memory. Also in these cases SAFE and SECURE coding practices should always be employed to avoid security issues.

就ISO C标准(该语言的官方定义)而言，在其边界之外访问数组具有“未定义行为”。字面意思是:

行为，在使用不可移植或错误的程序构造或 错误的数据，本标准没有规定 需求

一个非规范性的注释对此进行了扩展:

可能的未定义行为包括忽略情况 翻译过程中的行为完全无法预测结果 或以文件化的方式执行程序的特点 环境(有或没有发出诊断消息)，到 终止翻译或执行(通过发出 诊断消息)。

这就是理论。现实是什么?

在“最佳”情况下，您将访问一些内存，这些内存要么属于当前运行的程序(这可能导致您的程序行为不正常)，要么不属于当前运行的程序(这可能导致您的程序因分段错误而崩溃)。或者你可能会尝试写入程序拥有的内存，但它被标记为只读;这也可能导致您的程序崩溃。

That's assuming your program is running under an operating system that attempts to protect concurrently running processes from each other. If your code is running on the "bare metal", say if it's part of an OS kernel or an embedded system, then there is no such protection; your misbehaving code is what was supposed to provide that protection. In that case, the possibilities for damage are considerably greater, including, in some cases, physical damage to the hardware (or to things or people nearby).

即使在受保护的操作系统环境中，保护也不总是100%。例如，有些操作系统错误允许非特权程序获得根(管理)访问权限。即使使用普通用户权限，出现故障的程序也会消耗过多的资源(CPU、内存、磁盘)，可能导致整个系统瘫痪。许多恶意软件(病毒等)利用缓冲区溢出来获得对系统的未经授权的访问。

(一个历史上的例子:我听说在一些具有核心内存的旧系统上，在一个紧密循环中重复访问单个内存位置可能会导致内存块融化。其他的可能性包括损坏CRT显示器，以驱动器柜的谐波频率移动磁盘驱动器的读写头，导致它走过桌子，掉到地板上。)

而且还要担心天网。

底线是这样的:如果你可以编写一个程序故意做一些不好的事情，那么至少在理论上，一个有bug的程序可能会意外地做同样的事情。

实际上，在MacOS X系统上运行的有bug的程序不太可能出现比崩溃更严重的情况。但是完全阻止有bug的代码做一些非常糟糕的事情是不可能的。

除了你自己的程序，我不认为你会破坏任何东西，在最坏的情况下，你会尝试从一个内存地址读取或写入一个页面，内核没有分配给你的进程，产生适当的异常并被杀死(我的意思是，你的进程)。

在测试代码时，您可能想尝试使用Valgrind中的memcheck工具——它不会捕获堆栈框架内的单个数组边界违规，但它应该捕获许多其他类型的内存问题，包括那些会导致单个函数范围之外的微妙、更广泛的问题的问题。

摘自手册:

Memcheck is a memory error detector. It can detect the following problems that are common in C and C++ programs. Accessing memory you shouldn't, e.g. overrunning and underrunning heap blocks, overrunning the top of the stack, and accessing memory after it has been freed. Using undefined values, i.e. values that have not been initialised, or that have been derived from other undefined values. Incorrect freeing of heap memory, such as double-freeing heap blocks, or mismatched use of malloc/new/new[] versus free/delete/delete[] Overlapping src and dst pointers in memcpy and related functions. Memory leaks.

ETA:不过，正如卡兹的回答所说，它不是万能的，并且并不总是提供最有帮助的输出，特别是当您使用令人兴奋的访问模式时。

Objective-C中的nsarray被分配一个特定的内存块。超过数组的边界意味着您将访问没有分配给数组的内存。这意味着:

This memory can have any value. There's no way of knowing if the data is valid based on your data type. This memory may contain sensitive information such as private keys or other user credentials. The memory address may be invalid or protected. The memory can have a changing value because it's being accessed by another program or thread. Other things use memory address space, such as memory-mapped ports. Writing data to unknown memory address can crash your program, overwrite OS memory space, and generally cause the sun to implode.

从程序的角度来看，您总是想知道代码何时超出了数组的边界。这可能导致返回未知值，导致应用程序崩溃或提供无效数据。