在听StackOverflow播客的时候,经常有人说“真正的程序员”是用C语言编写的,而C语言的速度要快得多,因为它“接近机器”。把前面的断言留到另一篇文章,C有什么特别之处,使它比其他语言更快?或者换句话说:什么能阻止其他语言编译成二进制代码,使其运行速度与C语言一样快?
当前回答
主要的因素是它是一种静态类型的语言,可以编译为机器代码。此外,由于它是一种低级语言,它通常不会做任何您不让它做的事情。
这些是我想到的其他一些因素。
Variables are not automatically initialized No bounds checking on arrays Unchecked pointer manipulation No integer overflow checking Statically-typed variables Function calls are static (unless you use function pointers) Compiler writers have had lots of time to improve the optimizing code. Also, people program in C for the purpose of getting the best performance, so there's pressure to optimize the code. Parts of the language specification are implementation-defined, so compilers are free to do things in the most optimal way
大多数静态类型语言的编译速度可以和C语言一样快,甚至比C语言更快,特别是如果它们可以假设C语言因为指针别名等原因而不能这样做的话。
其他回答
C的设计者们已经做出了取舍。也就是说,他们决定把速度放在安全之上。C不会
检查数组下标边界 检查未初始化的变量值 检查内存泄漏 检查空指针解引用
当你索引到一个数组时,在Java中,它接受虚拟机中的一些方法调用,绑定检查和其他健全检查。这是有效的,绝对没问题,因为它在应有的地方增加了安全性。但是在C语言中,即使是非常微不足道的东西也不会被放在安全的地方。例如,C不要求memcpy检查要复制的区域是否重叠。它并不是一种用于编写大型商业应用程序的语言。
但是这些设计决策并不是C语言中的bug。它们是被设计出来的,因为它允许编译器和库编写者从计算机中获得每一点性能。下面是C语言的精神——C语言的基本原理文档是这样解释的:
C code can be non-portable. Although it strove to give programmers the opportunity to write truly portable programs, the Committee did not want to force programmers into writing portably, to preclude the use of C as a ``high-level assembler'': the ability to write machine-specific code is one of the strengths of C. Keep the spirit of C. The Committee kept as a major goal to preserve the traditional spirit of C. There are many facets of the spirit of C, but the essence is a community sentiment of the underlying principles upon which the C language is based. Some of the facets of the spirit of C can be summarized in phrases like Trust the programmer. Don't prevent the programmer from doing what needs to be done. Keep the language small and simple. Provide only one way to do an operation. Make it fast, even if it is not guaranteed to be portable. The last proverb needs a little explanation. The potential for efficient code generation is one of the most important strengths of C. To help ensure that no code explosion occurs for what appears to be a very simple operation, many operations are defined to be how the target machine's hardware does it rather than by a general abstract rule. An example of this willingness to live with what the machine does can be seen in the rules that govern the widening of char objects for use in expressions: whether the values of char objects widen to signed or unsigned quantities typically depends on which byte operation is more efficient on the target machine.
这是自动和手动的区别,高级语言是抽象的,因此是自动化的。C/ c++是人工控制和处理的,甚至错误检查代码有时也是人工劳动。
C和c++也是编译语言,这意味着没有任何一种语言可以在任何地方运行,这些语言必须针对您使用的硬件进行微调,从而增加了额外的隐患。尽管现在C/ c++编译器在所有平台上变得越来越普遍,这有点令人不安。您可以在平台之间进行交叉编译。这仍然不是一个到处运行的情况,你基本上是在指示编译器a针对编译器B编译相同的代码,不同的架构。
归根结底,C语言并不意味着容易理解或推理,这也是为什么它们被称为系统语言。他们出现在所有高层次抽象的废话之前。这也是为什么它们不用于前端web编程。他们只是不适合这项任务,他们的意思是解决传统语言工具无法解决的复杂问题。
这就是为什么你会得到一些疯狂的东西(微架构、驱动程序、量子物理、AAA游戏、操作系统),这些东西C和c++非常适合。速度和数据处理是主要领域。
C语言速度很快,因为它是原生编译的低级语言。但是C不是最快的。递归斐波那契基准测试表明Rust、Crystal和Nim可以更快。
甚至C和c++之间的差异有时也会很大。
当你为一个对象分配内存,调用构造函数,在字边界上对齐内存等等,程序最终会经历很多开销,这些开销都是从程序员那里抽象出来的。
C迫使您查看程序所做的每一件事,通常是非常精细的细节。这使得编写执行大量与当前目标无关的任务的代码变得更加困难(尽管并非完全不可能)。
因此,例如在BASIC程序中,你可以使用INPUT关键字从STDIN读取字符串并自动为其变量分配内存,在C中,程序员通常已经分配了内存,并可以控制诸如程序是否阻塞I/O,以及它是否在获得所需信息后停止读取输入或继续读取字符到行尾等事情。
C also performs a lot less error-checking than other languages, presuming the programmer knows what they're doing. So whereas in PHP if you declare a string $myStr = getInput(); and go on to reference $myStr[20], but the input was only 10 characters long, PHP will catch this and safely return to you a blank string. C assumes that you've either allocated enough memory to hold data past the end of the string or that you know what information comes after the string and are trying to reference that instead. These small factors have a huge impact on overhead in aggregate.
一些c++算法比C快,其他语言中的算法或设计模式的一些实现可能比C快。
当人们说C语言很快,然后转向谈论其他语言时,他们通常是在用C语言的性能作为基准。