使用 ssize_t 与 int [英] Using ssize_t vs int

问题描述

我有一个函数，我可以用 一种 四种可能的方式编写它:

I've got a function which I can write in one of four possible ways:

    int do_or_die(int retval);
    int do_or_die(ssize_t retval);
    ssize_t do_or_die(int retval);   
    ssize_t do_or_die(ssize_t retval);   

<小时>

然后它会被两种库函数调用:

    written = do_or_die(write(...)); // POSIX write returns ssize_t
    printed = do_or_die(printf(...)); // printf returns int

问题

• 我应该使用哪个原型?
• 我应该给 written 和 printed 哪些类型?

Questions

• Which prototype should I use?
• What types should I give to written and printed?

我希望拥有最强大和最标准的代码，同时仍然只有一个 do_or_die 函数.

I want to have the most robust and standard code, while still having just one do_or_die function.

在这种情况下我使用的是 C99，但如果 C11 的答案不同，那么我也想知道这一点，以备将来使用.

I am using C99 in this case, but if answer is different for C11, then I'd like to know that too, for future.

推荐答案

POSIX 标准不保证 sizeof(int) >= sizeof(ssize_t)，反之亦然.通常 ssize_t 大于 int，但 C99 中安全且可移植的选项是使用 intmax_t 代替参数和返回值.

There's no guarantee in the POSIX standard that sizeof(int) >= sizeof(ssize_t), nor the other way around. Typically ssize_t is larger than int, but the safe and portable option in C99 is to use intmax_t instead for the argument and the return value.

您拥有 wrt 的唯一保证.int 和 ssize_t 的关系是:

The only guarantees you have wrt. the relationship between int and ssize_t are:

• int 可以根据 ISO C 存储至少 [-2^15 ... 2^15-1] 范围内的值
• ssize_t 可以根据 POSIX 存储至少 [-1 ... 2^15-1] 范围内的值(参见 _POSIX_SSIZE_MAX).
• int can store values of at least the range [-2^15 ... 2^15-1] per ISO C
• ssize_t can store values of at least the range [-1 ... 2^15-1] per POSIX (see _POSIX_SSIZE_MAX).

(有趣的是，甚至不能保证 ssize_t 可以存储其正数范围的负数.它不是带符号的 size_t，而是大小类型"" 带有错误值.)

(Interestingly, there isn't even a guarantee that ssize_t can store the negative counterparts of its positive range. It's not a signed size_t, but a "size type" with an error value.)

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