每个人都知道Dijkstra的《致编辑的信》:goto语句被认为是有害的(这里。html transcript和这里。pdf)，从那时起，就有一种强大的推动力，尽可能避免使用goto语句。虽然可以使用goto来生成不可维护的、庞大的代码，但它仍然存在于现代编程语言中。即使Scheme中先进的连续控制结构也可以被描述为复杂的后向。
在什么情况下需要使用goto?什么时候最好避免?
作为一个后续问题:C提供了一对函数setjmp()和longjmp()，它们不仅提供了在当前堆栈帧内进行跳转的能力，还提供了在任何调用帧内进行跳转的能力。这些应该被认为和goto一样危险吗?更危险?
Dijkstra自己也对这个头衔感到后悔，因为这不是他的责任。在EWD1308的结尾(也在这里。pdf)，他写道:
Finally a short story for the record.
In 1968, the Communications of the ACM
published a text of mine under the
title "The goto statement considered
harmful", which in later years would
be most frequently referenced,
regrettably, however, often by authors
who had seen no more of it than its
title, which became a cornerstone of
my fame by becoming a template: we
would see all sorts of articles under
the title "X considered harmful" for
almost any X, including one titled
"Dijkstra considered harmful". But
what had happened? I had submitted a
paper under the title "A case against
the goto statement", which, in order
to speed up its publication, the
editor had changed into a "letter to
the Editor", and in the process he had
given it a new title of his own
invention! The editor was Niklaus
Wirth.
Donald E. Knuth写了一篇关于这个主题的经典论文，它与Dijkstra的论文相匹配，那就是结构化编程与语句。阅读既有助于重建上下文，也有助于对主题的非教条性理解。在本文中，Dijkstra对这个案例的观点被报道，并且更加强烈:
Donald E. Knuth:我相信通过呈现这样一个
事实上，我并不是不同意
Dijkstra的观点，因为
他最近写道:
“请不要落入。
相信我是可怕的
教条的关于[去]的教条的
声明)。我觉得很不舒服
感觉别人在做
宗教出来了，好像
编程的概念问题
只用一个小技巧就能解决，用什么
一种简单的编码纪律!”
我们已经讨论过这个问题了，我坚持我的观点。
此外，我受够了人们将高级语言结构描述为“伪装的goto”，因为他们显然根本没有抓住重点。例如:
即使Scheme中先进的连续控制结构也可以被描述为复杂的后向。
那完全是胡说八道。每个控制结构都可以在goto方面实现，但这个观察完全是微不足道和无用的。Goto被认为是有害的，因为它的积极影响，而是因为它的消极后果，这些已经被结构化编程消除了。
Similarly, saying “GOTO is a tool, and as all tools, it can be used and abused” is completely off the mark. No modern construction worker would use a rock and claim it “is a tool.” Rocks have been replaced by hammers. goto has been replaced by control structures. If the construction worker were stranded in the wild without a hammer, of course he would use a rock instead. If a programmer has to use an inferior programming language that doesn't have feature X, well, of course she may have to use goto instead. But if she uses it anywhere else instead of the appropriate language feature she clearly hasn't understood the language properly and uses it wrongly. It's really as simple as that.
Since I began doing a few things in the linux kernel, gotos don't bother me so much as they once did. At first I was sort of horrified to see they (kernel guys) added gotos into my code. I've since become accustomed to the use of gotos, in some limited contexts, and will now occasionally use them myself. Typically, it's a goto that jumps to the end of a function to do some kind of cleanup and bail out, rather than duplicating that same cleanup and bailout in several places in the function. And typically, it's not something large enough to hand off to another function -- e.g. freeing some locally (k)malloc'ed variables is a typical case.
I've written code that used setjmp/longjmp only once. It was in a MIDI drum sequencer program. Playback happened in a separate process from all user interaction, and the playback process used shared memory with the UI process to get the limited info it needed to do the playback. When the user wanted to stop playback, the playback process just did a longjmp "back to the beginning" to start over, rather than some complicated unwinding of wherever it happened to be executing when the user wanted it to stop. It worked great, was simple, and I never had any problems or bugs related to it in that instance.
Setjmp /longjmp有它们自己的位置——但那个位置是你不太可能只在很长一段时间内访问一次的地方。
编辑:我只是看了一下代码。实际上，我使用的是siglongjmp()，而不是longjmp(不是说这是一个大问题，但我已经忘记了siglongjmp的存在。)
