Solution to error when accessing array elements in PHP double quotes PHP skills

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I am currently developing a WeChat public account. In an interface for sending graphics and text, I need to splice array elements into an XML string

foreach ($itemArr as $key => $value){ 
  $items .= "<item> 
  <Title><![CDATA[$value[&#39;title&#39;]]]></Title>  
  <Description><![CDATA[[$value[&#39;description&#39;]]]></Description> 
  <PicUrl><![CDATA[$value[&#39;picUrl&#39;]]]></PicUrl> 
  <Url><![CDATA[$value[&#39;url&#39;]]]></Url> 
  </item>"; 
}

The result was the following error message:

Parse error: syntax error, unexpected '' (T_ENCAPSED_AND_WHITESPACE), expecting identifier (T_STRING) or variable (T_VARIABLE) or number (T_NUM_STRING) in D:\hhp\wamp\www\weixin\wx_sample.php on line 146

From the error message It seems that it is a problem with single quotation marks. After decisively removing it, there is no error. However, I am confused. Shouldn't quotes be added to array elements whose subscripts are strings? I went to the PHP official manual to check the description of arrays. There is a paragraph like this:

$arr = array('fruit' => 'apple', 'veggie' => 'carrot'); 
// This will not work, and will result in a parse error, such as: 
// Parse error: parse error, expecting T_STRING' or T_VARIABLE' or T_NUM_STRING' 
// This of course applies to using superglobals in strings as well 
print "Hello $arr['fruit']"; 
print "Hello $_GET['foo']";

There are two wrong ways of writing. When an ordinary When an array variable or superglobal array variable is enclosed in double quotes, referencing the array element whose index is a string, the index string should not be added with single quotes. So what is the correct way to write it? So I continued to search the official manual and found the following statement:

$arr = array('fruit' => 'apple', 'veggie' => 'carrot');

// This defines a constant to demonstrate what's going on. The value 'veggie'
// is assigned to a constant named fruit.
define('fruit', 'veggie');

// The following is okay, as it's inside a string. Constants are not looked for// within strings, so no E_NOTICE occurs hereprint "Hello $arr[fruit]";   // Hello apple// With one exception: braces surrounding arrays within strings allows constants// to be interpretedprint "Hello {$arr[fruit]}";  // Hello carrotprint "Hello {$arr['fruit']}"; // Hello apple

$arr = array('fruit' => 'apple', 'veggie' => 'carrot');

// This defines a constant to demonstrate what's going on. The value 'veggie'
// is assigned to a constant named fruit.
define('fruit', 'veggie');

// The following is okay, as it's inside a string. Constants are not looked for
// within strings, so no E_NOTICE occurs here
print "Hello $arr[fruit]";   // Hello apple

// With one exception: braces surrounding arrays within strings allows constants
// to be interpreted
print "Hello {$arr[fruit]}";  // Hello carrot
print "Hello {$arr['fruit']}"; // Hello apple

There are three correct ways of writing:

The first way of writing the index string does not add any quotation marks. At this time, it means to get the array element whose index is the string fruit and output apple.

The second way of writing the index string is without adding any quotation marks, and at the same time, the array variable is wrapped in a pair of curly braces { }. At this time, fruit It actually represents a constant, not a string, so it means getting the array element whose index is the fruit constant value. The value of the constant fruit is veggie, so carrot is output.

The third way of writing is to quote the string by not only adding single quotes, but also wrapping the array variable with a pair of curly braces { }. This way When it means to get the array element whose index is the string fruit, output apple. Later I continued to search and found this piece of code:

// Incorrect. This works but also throws a PHP error of level E_NOTICE because 
// of an undefined constant named fruit 
//  
// Notice: Use of undefined constant fruit - assumed 'fruit' in... 
print $arr[fruit];  // apple 
<pre name="code" class="php">print $arr[&#39;fruit&#39;]; // apple

##

// This defines a constant to demonstrate what's going on. The value 'veggie'// is assigned to a constant named fruit.define('fruit', 'veggie');// Notice the difference nowprint $arr[fruit]; // carrot

print $arr['fruit']; // apple

In normal In this case, when the array variable is not surrounded by double quotes, the output results are consistent whether or not single quotes are added to the index string. However, when a constant with the same name as the index string fruit is defined, the index string without single quotes will appear. The output becomes carrot, but adding single quotes is still apple.

Conclusion:

1. When the array variable is not enclosed in double quotes,

(1) The index string with single quotes represents the string itself

<pre name="code" class="php">$arr[&#39;fruit&#39;]

(2) The index string without single quotes represents a constant, When the constant is undefined, it is parsed as a string, which is equivalent to adding single quotes.

$arr[fruit]

2. When the array variable is enclosed in double quotes,

(1) The index string without single quotes represents the string itself

"$arr[fruit]"

(2) The array variable with curly braces represents a constant with the same name as the string

"{$arr[fruit]}"

(3) Add single quotes to the index string and add curly braces to the array variable to represent the string itself

<pre name="code" class="php"><pre name="code" class="php">"{$arr[&#39;fruit&#39;]}"

(4) The index string is enclosed in single quotes and the array variable is not enclosed in curly braces, which is an incorrect way of writing. The error is reported: Parse error: parse error, expecting T_STRING' or T_VARIABLE' or T_NUM_STRING'

<pre name="code" class="php"><pre name="code" class="php">"$arr[&#39;fruit&#39;]"

Attachment: PHP manual array description URL

http://php.net/manual/zh/language.types.array. php

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