C语言程序设计：从一个角度汇编点++ i和i = i + 1的区别？ [英] C Programming: difference between ++i and i=i+1 from an assembler point of view?

问题描述

这是一个面试问题。我说他们是一样的，但是这被判定不正确的响应。但从汇编点，是否有任何可以想象的区别？我编使用默认的gcc的优化和-S看看汇编器输出的两个短的C程序，它们是相同的。

This was an interview question. I said they were the same, but this was adjudged an incorrect response. From the assembler point of view, is there any imaginable difference? I have compiled two short C programs using default gcc optimization and -S to see the assembler output, and they are the same.

推荐答案

面试官可能是想答案是这样的：

The interviewer may have wanted an answer something like this:

I = I + 1 将要载入 i的值，添加一个，然后存储结果返回给 I 。相比之下， ++我可以简单地使用单个汇编指令，所以理论上它可能是更有效的增加值。然而，大多数的编译器将优化程差，并将所产生的code将是完全一样的。

i=i+1 will have to load the value of i, add one to it, and then store the result back to i. In contrast, ++i may simply increment the value using a single assembly instruction, so in theory it could be more efficient. However, most compilers will optimize away the difference, and the generated code will be exactly the same.

FWIW，你知道怎么看装配让你比我有采访多年来人们90％的更好​​的程序员的事实。以安慰的事实，你不会有谁面试你无能的失败者工作。

FWIW, the fact that you know how to look at assembly makes you a better programmer than 90% of the people I've had to interview over the years. Take solace in the fact that you won't have to work with the clueless loser who interviewed you.

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