Question

我在Services_JSON php库中找到了这堆代码：

if ($this->use & SERVICES_JSON_LOOSE_TYPE) {
    $stk = array(SERVICES_JSON_IN_OBJ);
    $obj = array();
} else {
    $stk = array(SERVICES_JSON_IN_OBJ);
    $obj = new stdClass();
}

我的问题是关于第一行。单个“＆amp;”运算符有什么作用？

Answer 1

这是PHP按位AND运算符：http://php.net/manual/en/language.operators.bitwise.php

Answer 2

＆安培;＆安培;意味着＆＃34;和＆＃34; （逻辑运算符）但是单个＆＃34;＆amp;＆＃34;是一个按位运算符，它对位进行二进制比较。

以下是php.net的手册： http://us2.php.net/manual/en/language.operators.bitwise.php

Answer 3

不仅要解释什么＆amp;但是，在这种情况下，这个按位和运算符可能用于查看

<?php
define('SOME_FLAG', 1);
define('SERVICES_JSON_LOOSE_TYPE', 2);
define('ANOTHER_FLAG', 4);

foo(0);
foo(7);
foo(SERVICES_JSON_LOOSE_TYPE|ANOTHER_FLAG);

function foo($value) {
    echo "foo($value)\n";

    bar($value, SOME_FLAG);
    bar($value, SERVICES_JSON_LOOSE_TYPE);
    bar($value, ANOTHER_FLAG);

    if ( $value & SOME_FLAG ) {
        echo "  SOME_FLAG set\n";
    }
    else {
        echo "  SOME_FLAG NOT set\n";
    }

    if ( $value & SERVICES_JSON_LOOSE_TYPE ) {
        echo "  SERVICES_JSON_LOOSE_TYPE set\n";
    }
    else {
        echo "  SERVICES_JSON_LOOSE_TYPE NOT set\n";
    }

    if ( $value & ANOTHER_FLAG ) {
        echo "  ANOTHER_FLAG set\n";
    }
    else {
        echo "  ANOTHER_FLAG NOT set\n";
    }
    echo "\n";
} 

function bar($value, $flag) {
    printf("  value|  %08s (%d)\n", decbin($value), $value);
    printf("  flag |& %08s (%d)\n", decbin($flag), $flag);
    printf("  and  |= %08s (%d)\n", decbin($value & $flag), $value & $flag);
    echo "\n";
}

输出

foo(0)
  value|  00000000 (0)
  flag |& 00000001 (1)
  and  |= 00000000 (0)

  value|  00000000 (0)
  flag |& 00000010 (2)
  and  |= 00000000 (0)

  value|  00000000 (0)
  flag |& 00000100 (4)
  and  |= 00000000 (0)

  SOME_FLAG NOT set
  SERVICES_JSON_LOOSE_TYPE NOT set
  ANOTHER_FLAG NOT set

foo(7)
  value|  00000111 (7)
  flag |& 00000001 (1)
  and  |= 00000001 (1)

  value|  00000111 (7)
  flag |& 00000010 (2)
  and  |= 00000010 (2)

  value|  00000111 (7)
  flag |& 00000100 (4)
  and  |= 00000100 (4)

  SOME_FLAG set
  SERVICES_JSON_LOOSE_TYPE set
  ANOTHER_FLAG set

foo(6)
  value|  00000110 (6)
  flag |& 00000001 (1)
  and  |= 00000000 (0)

  value|  00000110 (6)
  flag |& 00000010 (2)
  and  |= 00000010 (2)

  value|  00000110 (6)
  flag |& 00000100 (4)
  and  |= 00000100 (4)

  SOME_FLAG NOT set
  SERVICES_JSON_LOOSE_TYPE set
  ANOTHER_FLAG set

这是一种测试是否在某个值中设置某个标志的方法看看php文档，例如preg_match_all的文档：

 flags
    Can be a combination of the following flags [...]
    PREG_PATTERN_ORDER [...]
    PREG_SET_ORDER [...]
    PREG_OFFSET_CAPTURE [...]

您将在文档中多次发现此Can be a combination of the following flags...事件。这些函数/方法背后的代码完全使用按位和运算符进行检查。

“＆安培;”运算符在条件语句中

3 个答案: