Question

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？我在搜索中找不到一个例子。

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

感谢您的帮助。

Answer 1

它被称为Complex (curly) syntax

这不称为复杂，因为语法很复杂，但因为它允许使用复杂的表达式。

可以通过此语法包含任何具有字符串表示形式的标量变量，数组元素或对象属性。只需以与字符串外部相同的方式编写表达式，然后将其包装在{和}中。由于{无法转义，因此仅当$紧跟{时，才会识别此语法。使用{\ $获取文字{$。一些例子说清楚：

<?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()}";
?>

PHP语法$ {＆＃34; field＆＃34;}

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