对于积分/运算类型C和C尺寸保证++ [英] size guarantee for integral/arithmetic types in C and C++

问题描述

我知道C ++标准明确保障的只有字符，符号字符和<$ C $大小C> unsigned char型。此外，它提供了保证，比如，短至少是一样大的字符， INT 大如短等，但有关，绝对值没有明确保证说，的sizeof（INT）。这是在我脑海中的信息，我与它幸福地生活在一起。前一段时间，但是，我碰到一个注释进来SO（无法找到它），在C 长是保证至少有4个字节，即要求由C ++继承。是这样吗？如果是这样，我们还有什么其他的隐性担保算术类型的C ++的大小？请注意，我绝对不感兴趣的实际的跨越在这个问题上不同的平台保障，只是理论的人。

I know that the C++ standard explicitly guarantees the size of only char, signed char and unsigned char. Also it gives guarantees that, say, short is at least as big as char, int as big as short etc. But no explicit guarantees about absolute value of, say, sizeof(int). This was the info in my head and I lived happily with it. Some time ago, however, I came across a comment in SO (can't find it) that in C long is guaranteed to be at least 4 bytes, and that requirement is "inherited" by C++. Is that the case? If so, what other implicit guarantees do we have for the sizes of arithmetic types in C++? Please note that I am absolutely not interested in practical guarantees across different platforms in this question, just theoretical ones.

推荐答案

18.2.2保证＆LT; climits＆GT; 具有相同的内容的C库头＆LT; limits.h中方式＆gt;

18.2.2 guarantees that <climits> has the same contents as the C library header <limits.h>.

在ISO C90标准是棘手弄个，这是考虑到C ++依赖于一种耻辱，但部分数字限制（随机草案一追查有一次编号为2.2.4.2，并撒谎左右）给出了最小值为 INT_MAX 等在＆LT常数; limits.h中＆GT; 。例如 ULONG_MAX 必须至少4294967295，从中我们推断的宽度长至少是32位。

The ISO C90 standard is tricky to get hold of, which is a shame considering that C++ relies on it, but the section "Numerical limits" (numbered 2.2.4.2 in a random draft I tracked down on one occasion and have lying around) gives minimum values for the INT_MAX etc. constants in <limits.h>. For example ULONG_MAX must be at least 4294967295, from which we deduce that the width of long is at least 32 bits.

有在C99标准类似的限制，当然这些都不是用C ++ 03中引用的那些。

There are similar restrictions in the C99 standard, but of course those aren't the ones referenced by C++03.

这确实的不的保证长至少是4个字节，因为在C和C ++字节基本上是定义为CHAR ，并且不保证 CHAR_BIT 是用C或C ++ 8。 CHAR_BIT == 8 是由两个POSIX和Windows保障。

This does not guarantee that long is at least 4 bytes, since in C and C++ "byte" is basically defined to mean "char", and it is not guaranteed that CHAR_BIT is 8 in C or C++. CHAR_BIT == 8 is guaranteed by both POSIX and Windows.

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