PHP 语法 ${"field"} [重复]答案

【问题标题】：PHP Syntax ${"field"} [duplicate]PHP 语法 ${"field"} [重复]
【发布时间】：2015-06-05 12:01:02
【问题描述】：

我不认识 ${"item_$i"}; 的 PHP 语法； item_$i 可以是 item_1 到 item_6。 ${ } 在作业中表示什么？我在搜索中找不到示例。

if($cl_name=='A') $data = ${"item_$i"};

感谢您的帮助。

【问题讨论】：

标签： php string variables

【解决方案1】：

它叫Complex (curly) syntax

这不是因为语法复杂，而是因为它允许使用复杂的表达式。

任何标量变量、数组元素或具有字符串表示的对象属性都可以通过此语法包含在内。只需将表达式写成与它出现在字符串之外的相同方式，然后将其包装在 { 和 } 中。由于 { 无法转义，因此只有在 $ 紧跟 { 时才能识别此语法。使用 {\$ 获取文字 {$。一些例子来说明：

<?php
// Show all errors
error_reporting(E_ALL);

$great = 'fantastic';

// Won't work, outputs: This is { fantastic}
echo "This is { $great}";

// Works, outputs: This is fantastic
echo "This is {$great}";
echo "This is ${great}";

// Works
echo "This square is {$square->width}00 centimeters broad."; 


// Works, quoted keys only work using the curly brace syntax
echo "This works: {$arr['key']}";


// Works
echo "This works: {$arr[4][3]}";

// This is wrong for the same reason as $foo[bar] is wrong  outside a string.
// In other words, it will still work, but only because PHP first looks for a
// constant named foo; an error of level E_NOTICE (undefined constant) will be
// thrown.
echo "This is wrong: {$arr[foo][3]}"; 

// Works. When using multi-dimensional arrays, always use braces around arrays
// when inside of strings
echo "This works: {$arr['foo'][3]}";

// Works.
echo "This works: " . $arr['foo'][3];

echo "This works too: {$obj->values[3]->name}";

echo "This is the value of the var named $name: {${$name}}";

echo "This is the value of the var named by the return value of getName(): {${getName()}}";

echo "This is the value of the var named by the return value of \$object->getName(): {${$object->getName()}}";

// Won't work, outputs: This is the return value of getName(): {getName()}
echo "This is the return value of getName(): {getName()}";
?>

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