在PHP中，0(int，零)等于"first".或“最后" (弦)? [英] In PHP, 0 (int, zero) is equal to "first" or "last" (strings)?

问题描述

我对自己正在使用的脚本中遇到的某些事情感到困惑.我有以下内容:

I'm confused by something I just ran into in a script I was working on. I had the following:

function getPart($part)
{
    $array = array('a', 'b', 'c');
    if ($part == 'first') $part = 0;
    if ($part == 'last') $part = count($array) - 1;
    if (isset($array[$part])) return $array[$part];
    return false;
}

$position = 0;
echo getPart($position);

因此，如果我尝试使用字符串"first"，则应该获得"a"作为输出.使用字符串"last"，我应该得到"c"，依此类推.当我使用PHP 5.3运行上述脚本时，出现"c" ...

So, if I were to try the string "first", I should get "a" as the output. With the string "last" I should get "c" and so on. When I run the script above, with PHP 5.3, I get "c" ...

困惑，我进行了快速测试...

Confused, I ran a quick test ...

var_dump(0 == 'first');
var_dump(0 == 'last');

两者都返回TRUE ... 为什么?我对此行为感到困惑！

Both return TRUE ... WHY??? I am so confused by this behavior!

推荐答案

如果您尝试将字符串与数字进行比较，PHP将尝试将字符串转换为数字.在这种情况下，它无法执行此操作，因为PHP无法将"first" 或"last" 转换为数字，因此只能将其转换为零.这使得检查0 == 0当然是正确的.如果希望PHP不尝试转换任何内容，请使用标识运算符===(因此，两个操作数必须具有相同的值并且具有相同的类型).

If you try to compare a string to a number, PHP will try to convert the string to a number. In this case, it fails to do so, since PHP can't convert "first" or "last" into a number, so it simply converts it to zero. This makes the check 0 == 0, which is, of course, true. Use the identity operator, ===, if you want PHP to not attempt to convert anything (so, the two operands must have the same value and be of the same type).

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