什么会导致 C++ 中的分段错误? [英] What can cause segmentation faults in C++?

问题描述

我注意到 C++ 中的分段错误的常见原因列表没有问题，所以我想我会添加它.

自然是社区 Wiki，因为没有一个正确答案.

我认为这可能对学习 C++ 的新程序员有用，如果您不同意，请随时关闭它.

解决方案

只有当你的操作系统有 MMU(
_{(来源:vistech.net 冠军)}

您主要对用户空间中发生的事情以及通向 SIGSEGV 的所有路径感兴趣.但内核空间也很有趣.

I noticed there's not question with a list of common causes of segmentation faults in C++, so I thought I'd add it.

Naturally it's community Wiki, since there's no one correct answer.

I think this might be useful for newer programmers learning C++, feel free to close it if you disagree.

解决方案

Segmentation fault is caused by bad accesses to memory, only if your OS has a MMU (Memory Management Unit). Otherwise, you won't get it but only strange behavior.

The virtual memory (the entire memory accessible to you = 2^(sizeof(pointer_type)*8) (ie: 2^num_bits_in_pointer_type)) is mapped to physical memory in units named pages or segments (paging superseded segmentation but they are still used).

Each page has some protection rights, if you try to read from a page with no-read access you'll get a segfault. If you try to write to a readonly location you'll get a SIGSEGV.

If you have an unitialized pointer and use it it may happen that it will point to another good location so you'll don't get a segfault. If you have a small array reading after it's bound may corrupt other memory areas if it doesn't get past the page boundary.

Also, since there are many pages, not all of them are really mapped. If you touch a non-mapped page you'll get a segfault. Actually, any access to a non mapped page will have to take into account copy on write, pages on swap, lazy loading, memory mapped files and other things. See this article on page fault handling, especially the second diagram there, posted here below too (but read the article for more explanations)

_{(source: champ at vistech.net)}

You are mainly interested in what happens in user space and all paths leading to SIGSEGV. but kernel space is also interesting.

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