PHP函数

bcmul：两个任意精度数字乘法计算

//bcmul(string $num1, string $num2, ?int $scale = null): string
echo bcmul('1.34747474747','35',3).'<br>';
echo bcmul('2','4');
//输出结果：47.161
           8

bcdiv：两个任意精度的数字除法计算

//bcdiv(string $num1, string $num2, ?int $scale = null): string
echo bcdiv('105','6.55957',3);
//输出结果：16.007

empty — 检查一个变量是否为空

//empty(mixed $var): bool
$arr='';
echo empty($arr)?'为空':'不为空';
//输出结果：为空

array_reverse：返回单元顺序相反的数组

//array_reverse(array $array, bool $preserve_keys = false): array
$cur = ['Hello','World'];
print_r(array_reverse($cur)) ;
//输出结果：Array ( [0] => World [1] => Hello )

array_keys:返回数组中部分的或所有的键名

//array_keys(array $array): array
//array_keys(array $array, mixed $search_value, bool $strict = false): array
$array = array(0 => 100, "color" => "red");
print_r(array_keys($array));
echo '<br>';
$array = array("blue", "red", "green", "blue", "blue");
print_r(array_keys($array, "blue"));
//输出结果分别为：Array ( [0] => 0 [1] => color )，Array ( [0] => 0 [1] => 3 [2] => 4 )