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!”


当前回答

用于调度的计算gotos通常比非常大的switch语句更容易理解。

对于错误和联合线程,我认为setcontext或setjmp(如果可用)是“更好的”。

其他回答

我只需要它在基本(即。VB, VBScript等)和批处理文件。然后我只将它用于错误处理。在Basic中,我倾向于只使用“on error goto”。在批处理文件中,我必须使用它,因为没有其他命令。然后,我只使用它们作为向前跳转到有意义的标签。

原论文应该被认为是“无条件GOTO被认为是有害的”。它特别提倡一种基于条件(if)和迭代(while)结构的编程形式,而不是早期代码常见的测试-跳转。Goto在某些语言或环境中仍然有用,因为这些语言或环境不存在适当的控制结构。

Using a goto makes it far too easy to write "spaghetti code" which is not particularly maintainable. The most important rule to follow is to write readable code, but of course it depends on what the goals of the project are. As a "best practice" avoiding a goto is a good idea. It's something extreme programming types would refer to as "code smell" because it indicates that you may be doing something wrong. Using a break while looping is remarkably similar to a goto, except it isn't a goto, but again is an indication that the code may not be optimal. This is why, I believe, it is also important to not find more modern programming loopholes which are essentially a goto by a different name.

在C语言中,goto只在当前函数的范围内工作,这倾向于本地化任何潜在的错误。Setjmp和longjmp要危险得多,它们是非本地的、复杂的、依赖于实现的。然而,在实践中,它们太模糊和不常见,不会引起很多问题。

我认为在C中goto的危险被大大夸大了。请记住,最初的goto参数发生在老式BASIC等语言的时代,初学者会编写这样的意大利面条代码:

3420 IF A > 2 THEN GOTO 1430

这里Linus描述了goto的适当用法:http://www.kernel.org/doc/Documentation/CodingStyle(第7章)。

Goto很有用,这里有一个用c++写的非常强大的开源象棋引擎stockfish的例子。goto只是跳过了一些条件检查(效率增益),如果没有goto语句,程序就必须这样做。如果goto语句标签位于goto声明之后,那么它们就非常无害且可读。