PHP 学习笔记
- 作用域灵活，整个方法内随便用，会有覆盖
empty方法，包含空值，无值以及0值的检测。 需要注意0值的判断，0值也认为是true
0值包含以下这些：
"" (an empty string)
0 (0 as an integer)
0.0 (0 as a float)
"0" (0 as a string)
NULL
FALSE
array() (an empty array)
$var; (a variable declared, but without a value)
http://www.cnblogs.com/ider/archive/2012/09/06/php_reference_issue.html 需要翻墙：http://schlueters.de/blog/archives/141-References-and-foreach.html
官方文档
foreach
(PHP 4, PHP 5, PHP 7) The foreach construct provides an easy way to iterate over arrays. foreach works only on arrays and objects, and will issue an error when you try to use it on a variable with a different data type or an uninitialized variable. There are two syntaxes:
foreach (array_expression as $value) statement foreach (array_expression as $key => $value) statement The first form loops over the array given by array_expression. On each iteration, the value of the current element is assigned to $value and the internal array pointer is advanced by one (so on the next iteration, you'll be looking at the next element).
The second form will additionally assign the current element's key to the $key variable on each iteration.
It is possible to customize object iteration.
Note: In PHP 5, when foreach first starts executing, the internal array pointer is automatically reset to the first element of the array. This means that you do not need to call reset() before a foreach loop. As foreach relies on the internal array pointer in PHP 5, changing it within the loop may lead to unexpected behavior. In PHP 7, foreach does not use the internal array pointer. In order to be able to directly modify array elements within the loop precede $value with &. In that case the value will be assigned by reference.
Warning Reference of a $value and the last array element remain even after the foreach loop. It is recommended to destroy it by unset(). Otherwise you will experience the following behavior:
// without an unset($value), $value is still a reference to the last item: $arr[3]
foreach ($arr as $key => $value) { // $arr[3] will be updated with each value from $arr... echo "{$key} => {$value} "; print_r($arr); } // ...until ultimately the second-to-last value is copied onto the last value
// output: // 0 => 2 Array ( [0] => 2, [1] => 4, [2] => 6, [3] => 2 ) // 1 => 4 Array ( [0] => 2, [1] => 4, [2] => 6, [3] => 4 ) // 2 => 6 Array ( [0] => 2, [1] => 4, [2] => 6, [3] => 6 ) // 3 => 6 Array ( [0] => 2, [1] => 4, [2] => 6, [3] => 6 ) ?>
http://www.w3school.com.cn/php/php_file_upload.asp http://blog.csdn.net/niushuai666/article/details/6672808
http://blog.csdn.net/ggh19/article/details/27081147
PsySH REPL工具，实用。