ç的qsort不能正常工作 [英] C qsort not working correctly

问题描述

我不知道我做错了，但下面code没有数组排序正确

I don't know what I'm doing wrong but the following code does not sort the array properly.

#include <stdio.h>
#include <stdlib.h>

int compare(const void* a, const void* b)
{
    return (*(int*)a - *(int*)b);
}

int main()
{
    int x[] = { -919238029,
            -889150029,
            -826670576,
            -579609061,
            -569653113,
            -305140505,
            -216823425,
            -193439331,
            -167683147,
            -49487019,
            -45223520,
            271789961,
            275570429,
            444855014,
            559132135,
            612312607,
            664554739,
            677860351,
            1005278191,
            1031629361,
            1089012280,
            1115952521,
            1521112993,
            1530518916,
            1907515865,
            1931470931,
            -1631034645,
            -1593702794,
            -1465300620,
            -1263094822
         };
    int i;

    qsort(x, 30, sizeof(int), compare);
    for(i = 0; i < 30; i ++)
        printf("%d\n", x[i]);

    return 0;
}

产生下面的输出：

produces the following output:

1521112993
1530518916
1907515865
1931470931
-1631034645
-1593702794
-1465300620
-1263094822
-919238029
-889150029
-826670576
-579609061
-569653113
-305140505
-216823425
-193439331
-167683147
-49487019
-45223520
271789961
275570429
444855014
559132135
612312607
664554739
677860351
1005278191
1031629361
1089012280
1115952521

我的意思是，这个问题/必须/是我比较功能。有人注意到有什么奇怪的？

I mean, the problem /must/ be in my compare function. Anybody notice anything strange?

推荐答案

是的，你的比较溢出。 （

Yeah, your "comparison" overflows. :(

当你从一个正数减去一个负数，你的结果不一定是正;如果它不能被重新在数据类型psented $ P $，它会环绕的另一侧。

When you subtract a negative number from a positive number, your result is not necessarily positive; if it can't be represented in the data type, it'll "wrap around" the other side.

如果您的整数只能从-8到7（4位）持有，那么什么时候你比较4到-4？结果发生
那么，你得到8，这是 1000 二进制，这是-8。因此，4小于-4。

If your integer can only hold from -8 to 7 (4 bits), then what happens when you compare 4 to -4?
Well, you get 8, which is 1000 in binary, which is -8. So 4 is less than -4.

不要做减法而不是比较，即使他们告诉你显得多么酷，这是在学校！

Don't do subtraction instead of comparison, even if they tell you "look how cool this is" at school!

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