You have to first realize that there's a big difference between a perceived memory leak and an actual memory leak. Very frequently analysis tools will report many red herrings, and label something as having been leaked (memory or resources such as handles etc) where it actually isn't. Often times this is due to the analysis tool's architecture. For example, certain analysis tools will report run time objects as memory leaks because it never sees those object freed. But the deallocation occurs in the runtime's shutdown code, which the analysis tool might not be able to see.

尽管如此，仍然会有一些时候，您会遇到实际的内存泄漏，这些泄漏要么很难发现，要么很难修复。现在的问题是，是否可以将它们保留在代码中?

The ideal answer is, "no, never." A more pragmatic answer may be "no, almost never." Very often in real life you have limited number of resources and time to resolve and endless list of tasks. When one of the tasks is eliminating memory leaks, the law of diminishing returns very often comes in to play. You could eliminate say 98% of all memory leaks in an application in a week, but the remaining 2% might take months. In some cases it might even be impossible to eliminate certain leaks because of the application's architecture without a major refactoring of code. You have to weigh the costs and benefits of eliminating the remaining 2%.

许多人似乎都有这样的印象:一旦释放内存，它就会立即返回到操作系统，可以被其他程序使用。

这不是真的。操作系统通常以4KiB页面管理内存。malloc和其他类型的内存管理从操作系统获取页面，并在它们认为合适的时候对它们进行子管理。free()很可能不会将页面返回给操作系统，前提是您的程序稍后会误用更多内存。

我并不是说free()从不将内存返回给操作系统。这是有可能发生的，特别是当您正在释放大量内存时。但这并不能保证。

重要的事实是:如果不释放不再需要的内存，那么进一步的malloc必然会消耗更多的内存。但是如果先释放，malloc可能会重新使用释放的内存。

这在实践中意味着什么?这意味着如果你知道你的程序从现在开始不再需要更多的内存(例如它在清理阶段)，释放内存就不是那么重要了。但是，如果程序稍后可能分配更多内存，则应该避免内存泄漏——特别是那些可能重复发生的内存泄漏。

关于为什么在终止前释放内存是不好的，请参阅这条评论了解更多细节。

评论者似乎不理解调用free()并不会自动允许其他程序使用释放的内存。但这就是这个答案的全部意义!

因此，为了说服人们，我将演示一个例子，其中free()没有什么好处。为了便于计算，我假设操作系统以4000字节的页面管理内存。

Suppose you allocate ten thousand 100-byte blocks (for simplicity I'll ignore the extra memory that would be required to manage these allocations). This consumes 1MB, or 250 pages. If you then free 9000 of these blocks at random, you're left with just 1000 blocks - but they're scattered all over the place. Statistically, about 5 of the pages will be empty. The other 245 will each have at least one allocated block in them. That amounts to 980KB of memory, that cannot possibly be reclaimed by the operating system - even though you now only have 100KB allocated!

另一方面，您现在可以malloc() 9000多个块，而不会增加程序占用的内存量。

即使free()在技术上可以将内存返回给操作系统，它也可能不会这样做。Free()需要在快速操作和节省内存之间取得平衡。此外，一个已经分配了大量内存然后释放它的程序很可能会再次这样做。web服务器需要处理一个又一个的请求——保持一些“松弛”的可用内存是有意义的，这样你就不需要一直向操作系统请求内存了。

一般情况下，如果遇到无法避免的内存泄漏，则需要更加认真地考虑对象所有权问题。

但对于你的问题，我的回答是在产品代码中，是的。在开发过程中，没有。这听起来可能有些倒退，但我的理由是:

In the situation you describe, where the memory is held until the end of the program, it's perfectly okay to not release it. Once your process exits, the OS will clean up anyway. In fact, it might make the user's experience better: In a game I've worked on, the programmers thought it would be cleaner to free all the memory before exiting, causing the shutdown of the program to take up to half a minute! A quick change that just called exit() instead made the process disappear immediately, and put the user back to the desktop where he wanted to be.

但是，您对调试工具的看法是正确的:它们会突然发作，而且所有的假阳性可能会使查找真正的内存泄漏变得很痛苦。正因为如此，总是编写释放内存的调试代码，并在发布时禁用它。

看来你对“内存泄漏”的定义是“我自己不清理的内存”。所有现代操作系统都会在程序退出时释放它。然而，由于这是一个c++问题，您可以简单地将所讨论的内存包装在适当的std::auto_ptr中，当它超出作用域时将调用delete。

从历史上看，在某些边缘情况下，它在某些操作系统上确实很重要。这些边缘情况在未来可能会存在。

Here's an example, on SunOS in the Sun 3 era, there was an issue if a process used exec (or more traditionally fork and then exec), the subsequent new process would inherit the same memory footprint as the parent and it could not be shrunk. If a parent process allocated 1/2 gig of memory and didn't free it before calling exec, the child process would start using that same 1/2 gig (even though it wasn't allocated). This behavior was best exhibited by SunTools (their default windowing system), which was a memory hog. Every app that it spawned was created via fork/exec and inherited SunTools footprint, quickly filling up swap space.

Some great answers here. To add another perspective to this question, I'll address a case where memory leak is not only acceptable but desirable: in Windows drivers environment the developer provides a set of callbacks that are being run by the OS whenever required. One of the callbacks is a 'Shutdown' callback, which runs prior to system being shut off/restarted. Unlike standard situations, not only memory release is not necessary (system will be off in a moment), it's even discouraged - to make the shutdown as fast as possible and prevent the overhead of memory management.