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
使用现代优化编译器,纯C程序不太可能比编译后的。net代码快得多,如果有的话。通过像。net这样的框架为开发人员提供的生产力提高,您可以在一天内完成过去用普通c语言需要几周或几个月才能完成的工作。再加上与开发人员的工资相比,硬件成本低廉,用高级语言编写这些东西并以任何缓慢的速度抛出硬件要便宜得多。
The reason Jeff and Joel talk about C being the "real programmer" language is because there is no hand-holding in C. You must allocate your own memory, deallocate that memory, do your own bounds-checking, etc. There's no such thing as new object(); There's no garbage collection, classes, OOP, entity frameworks, LINQ, properties, attributes, fields, or anything like that. You have to know things like pointer arithmetic and how to dereference a pointer. And, for that matter, know and understand what a pointer is. You have to know what a stack frame is and what the instruction pointer is. You have to know the memory model of the CPU architecture you're working on. There is a lot of implicit understanding of the architecture of a microcomputer (usually the microcomputer you're working on) when programming in C that simply is not present nor necessary when programming in something like C# or Java. All of that information has been off-loaded to the compiler (or VM) programmer.
其他回答
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。
1)正如其他人所说,C为你做的更少。没有初始化变量,没有数组边界检查,没有内存管理等。其他语言中的这些特性会消耗C语言不需要的内存和CPU周期。
2) Answers saying that C is less abstracted and therefore faster are only half correct I think. Technically speaking, if you had a "sufficiently advanced compiler" for language X, then language X could approach or equal the speed of C. The difference with C is that since it maps so obviously (if you've taken an architecture course) and directly to assembly language that even a naive compiler can do a decent job. For something like Python, you need a very advanced compiler to predict the probable types of objects and generate machine code on the fly -- C's semantics are simple enough that a simple compiler can do well.
令人惊讶的是,“C/ c++必须比Java快,因为Java是解释性的”的神话仍然活跃。有几年前的文章,也有最近的文章,用概念或测量来解释为什么这种情况并不总是如此。
当前的虚拟机实现(顺便说一下,不仅仅是JVM)可以利用程序执行期间收集的信息来动态地优化代码,使用各种技术:
将频繁的方法呈现给机器代码, 内联小方法, 锁紧调整
以及各种其他调整,这些调整是基于了解代码实际在做什么,以及它运行的环境的实际特征。
只需在您的IDE中逐步检查机器代码,您就会看到为什么它更快(如果它更快的话)。它省去了很多手把手的环节。很有可能你的Cxx也会被告知不要使用,在这种情况下,它应该是相同的。
编译器优化被高估了,就像几乎所有关于语言速度的看法一样。
优化生成的代码只会对热点代码产生影响,也就是说,没有函数调用(显式或隐式)的紧凑算法。在其他地方,收效甚微。
与其说C的速度快,不如说C的成本模型是透明的。如果一个C程序慢,它的慢是通过一个明显的方式:执行很多语句。与C语言中操作的代价相比,对对象(特别是反射)或字符串的高级操作可能具有不明显的代价。
标准ML(使用MLton编译器)和Objective Caml这两种语言通常编译成二进制文件的速度与C语言一样快。如果你检查一下基准测试游戏,你会发现对于一些基准测试,比如二叉树,OCaml版本比c更快(我没有找到任何MLton的条目)。但不要把枪战看得太严重;正如它所说的,它是一个游戏,结果通常反映了人们在调优代码上投入了多少精力。