阅读<Few lesser known tricks, quirks and features of C>

https://jorenar.com/blog/less-known-c
阅读并摘录了一些有趣的内容，如下：

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int x = 42;

int func() {
    int x = 3840;
    {
        extern int x;
        return x; // return 42;
    }
}

0 位字段

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struct bar {
    unsigned char x : 5;
    unsigned short  : 0;
    unsigned char y : 7;
}
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char pad pad      short boundary
 |    |   |        |
 v    v   v        v
 xxxxx000 00000000 yyyyyyy0

Duff’s device

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send(to, from, count)
    register short *to, *from;
    register count;
{
    register n = (count + 7) / 8;
    switch (count % 8) {
    case 0: do { *to = *from++;
    case 7:      *to = *from++;
    case 6:      *to = *from++;
    case 5:      *to = *from++;
    case 4:      *to = *from++;
    case 3:      *to = *from++;
    case 2:      *to = *from++;
    case 1:      *to = *from++;
            } while (--n > 0);
    }
}

idx[arr]

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// array[index]
boxes[products[myorder.product].box].weight;

// index[array]
myorder.product[products].box[boxes].weight;

负数组索引

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int *end = arr + (len - 1);
if (end[0] == VAL && end[-1] == VAL && end[-5] == VAL) {
    puts("Correct padding");
}

使用&&和||作为条件

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#include <ctype.h>
#include <stdio.h>
#include <stdbool.h>

int main(void)
{
    1 && puts("Hello");
    0 && puts("I won't");
    1 && puts("World!");
    0 && puts("be printed");
    1 || puts("I won't be printed either");
    0 || puts("But I will!");

    true && (9 > 2) && puts("9 is bigger than 2");

    isdigit('9') && puts("9 is a digit");
    isdigit('n') && puts("n is a digit") || puts("n is NOT a digit!");

    isalpha('a') && !puts("I'll be printed") || puts("But me AS WELL!");

    return 0;
}