在C中使用char作为小整数的优点/缺点 [英] Pros/cons to using char for small integers in C

问题描述

对C中的小整数使用 char 有什么不利吗？除了占用/内存优势之外还有什么优势吗？

Is there any disadvantage to using char for small integers in C? Are there any advantages other than the occupancy/memory benefit?

特别是，处理器可能会在 char上处理整数运算

好于或坏于（长 / 短） int ？

In particular, is the processor likely to cope with integer arithmetic on a char better or worse than it would on a (long/short) int?

我知道这将是处理器/系统/编译器特定的，但我希望在一般情况下得到答案，或者至少，32位Windows和Solaris的一般情况，是我目前正在研究的系统。我还假设已经处理了溢出/回绕问题等问题。

I know this will be processor/system/compiler specific, but I'm hoping for an answer in the general case, or, at least, the general case for 32-bit Windows and Solaris, being the systems I'm currently working on. I'm also assuming that things like overflow/wraparound issues have already been dealt with.

更新：Visual Studio 6.0实际上没有 stdint .h 正如Christoph所建议的那样。 Windows上的一个小基准测试（VS 6.0，调试版本，32位）和一些堆叠循环给出 int 和 long 提供类似的性能，大约是 char 的两倍。使用gcc在Linux上运行相同的测试同样将 int 和 long 视为相似，并且都比<$ c $更快c> char ，虽然差别不太明显。

Update: Visual Studio 6.0 doesn't actually have stdint.h as suggested by Christoph. A little benchmarking on Windows (VS 6.0, debug build, 32-bit) with a handful of stacked loops gives int and long as providing similar performance, which is about twice as fast as char. Running the same test on Linux with gcc similarly pegs int and long as similar, and both faster than char, although the difference is less pronounced.

作为旁注，我没有花太多时间看，但是 stdint的第一个实现.h for VS 6.0我发现（通过 Wikipedia ）将 uint_fast8_t 定义为 unsigned char ，尽管在​​我的测试中看起来似乎比较慢。因此，正如Christoph正确建议的那样，故事的寓意：总是基准！

As a side note, I've not spent much time looking, but the first implementation of stdint.h for VS 6.0 I found (via Wikipedia) defines uint_fast8_t as unsigned char, despite this seeming to be slower in my tests at least. Thus, the moral of the story, as Christoph rightly suggested: always benchmark!

推荐答案

C99增加了所谓的最快最低限度-width整数类型来解决这个问题。对于您感兴趣的范围，类型将是 int_fast8_t 和 uint_fast8_t ，可在<$中找到c $ c> stdint.h 。

C99 added so-called 'fastest' minimum-width integer types to solve this problem. For the range you're interested in, the types would be int_fast8_t and uint_fast8_t, which can be found in stdint.h.

请记住，可能没有性能提升（内存消耗的增加甚至可能会减慢速度下）;一如既往，基准！不要过早地或仅仅根据应该起作用的可能有缺陷的假设进行优化。

Keep in mind that there might be no performance gain (the increase in memory consumption might even slow things down); as always, benchmark! Don't optimize prematurely or solely on potentially flawed assumptions of what should work.

这篇关于在C中使用char作为小整数的优点/缺点的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！