当将STRCMP不会返回-1，0或1？ [英] When will strcmp not return -1, 0 or 1?

问题描述

从手册页：

该STRCMP（）和STRNCMP（）函数返回小于，等于少一个整数
  如果s1（或其前n个字节）被发现，或大于零，
  分别为小于，匹配，或者是大于s2

The strcmp() and strncmp() functions return an integer less than, equal to, or greater than zero if s1 (or the first n bytes thereof) is found, respectively, to be less than, to match, or be greater than s2.

例子$ C $（打印 -15 我的机器上，交换TEST1和TEST2反转值）C在C：

Example code in C (prints -15 on my machine, swapping test1 and test2 inverts the value):

#include <stdio.h>
#include <string.h>

int main() {
    char* test1 = "hello";
    char* test2 = "world";
    printf("%d\n", strcmp(test1, test2));
}

<击>我发现这个code （从<一所href=\"http://stackoverflow.com/questions/13560037/effcient-way-to-find-longest-duplicate-string-for-python-from-programming-pearl/13560449#13560449\">this问题）依靠的不是-1,0和1（它使用的qsort 的返回值等STRCMP是东西值）。对我来说，这是很可怕的风格和依赖于未记录的功能。

I found this code (taken from this question) that relies on the values of strcmp being something other than -1, 0 and 1 (it uses the return value in qsort). To me, this is terrible style and depends on undocumented features.

我想我有两个相关的问题：

I guess I have two, related questions:

• 有什么在C标准，定义什么返回值之外小于，大于或等于零？如果没有，什么是标准的实现呢？


• 是跨Linux，Windows和BSD系统？
一致的返回值

• Is there something in the C standard that defines what the return values are besides less than, greater than, or equal to zero? If not, what does the standard implementation do?
• Is the return value consistent across the Linux, Windows and the BSDs?

编辑：

离开我的电脑5分钟后，我意识到，其实也有与有问题的code没有错误。我打出了我阅读注释/应答前想通了部分，但我离开他们那里保持的评论相关。我认为这仍然是一个有趣的问题，并可能会导致对使用其他语言总是返回-1，0或1的程序员打嗝（例如Python的似乎要做到这一点，但它不记录这样）。

After leaving my computer for 5 minutes, I realized that there is in fact no error with the code in question. I struck out the parts that I figured out before reading the comments/answers, but I left them there to keep the comments relevant. I think this is still an interesting question and may cause hiccups for programmers used to other languages that always return -1, 0 or 1 (e.g. Python seems to do this, but it's not documented that way).

FWIW，我认为，依靠比记录的行为以外的东西是不好的风格。

FWIW, I think that relying on something other than the documented behavior is bad style.

推荐答案

在C99标准

7.21.4.2 The strcmp function

的 STRCMP 函数返回一个整数大于，等于或小于零，
相应地作为字符串指向S1大于，等于，或小于字符串s2指向到。

" The strcmp function returns an integer greater than, equal to, or less than zero, accordingly as the string pointed to by s1 is greater than, equal to, or less than the string pointed to by s2. "

这意味着标准不保证有关 1 ， 0 或 1 它可以根据操作系统的不同而不同。

It means standard doesn't guarantee about the -1 ,0or 1 it may vary according to operating systems.

你所得到的值是 W的和 ^ h 是 15的区别。

在你的情况你好和全球所以'H' - 'W'= -15℃; 0 和这就是为什么STRCMP retuns -15

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