最近在做微信公眾號(hào)開(kāi)發(fā),在一個(gè)發(fā)送圖文接口中,需要把數(shù)組元素拼接在XML字符串中
foreach ($itemArr as $key => $value){
$items .= "item>
Title>![CDATA[$value['title']]]>/Title>
Description>![CDATA[[$value['description']]]>/Description>
PicUrl>![CDATA[$value['picUrl']]]>/PicUrl>
Url>![CDATA[$value['url']]]>/Url>
/item>";
}
結(jié)果竟報(bào)如下錯(cuò)誤信息:
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
從錯(cuò)誤信息看是單引號(hào)的問(wèn)題,果斷去掉之后就沒(méi)報(bào)錯(cuò)了。然而我就納悶了,引用下標(biāo)為字符串的數(shù)組元素難道不該加引號(hào)嗎?到php官方手冊(cè)去查了關(guān)于數(shù)組的描述,有一段是這樣的:
$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']";
這里給出了兩種錯(cuò)誤的寫(xiě)法,當(dāng)一個(gè)普通數(shù)組變量或超全局?jǐn)?shù)組變量包含在雙引號(hào)中時(shí),引用索引為字符串的數(shù)組元素,索引字符串不應(yīng)該再添加單引號(hào)。那正確的寫(xiě)法是怎樣的呢?于是我繼續(xù)查找官方手冊(cè),找到如下說(shuō)法:
$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
這里給出了三種正確的寫(xiě)法:
第一種寫(xiě)法索引字符串不添加任何引號(hào),此時(shí)表示獲取索引為字符串fruit的數(shù)組元素,輸出apple。
第二種寫(xiě)法索引字符串也沒(méi)有添加任何引號(hào),同時(shí)將數(shù)組變量用一對(duì)花括號(hào){ }給包了起來(lái),此時(shí)fruit實(shí)際上表示一個(gè)常量,而不是一個(gè)字符串,因此表示獲取索引為fruit常量值的數(shù)組元素,常量fruit的值是veggie,所以輸出carrot。
第三種寫(xiě)法是引用字符串不但添加了單引號(hào),同時(shí)也將數(shù)組變量用一對(duì)花括號(hào){ }給包了起來(lái),此時(shí)表示獲取索引為字符串fruit的數(shù)組元素,輸出apple。
后來(lái)我繼續(xù)查找,發(fā)現(xiàn)這樣一段代碼:
// 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['fruit']; // 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 $arr['fruit']; // apple
在正常情況下,數(shù)組變量沒(méi)有被雙引號(hào)包圍時(shí),是否給索引字符串加上單引號(hào)輸出結(jié)果都一致時(shí)apple,但是當(dāng)定義一個(gè)與索引字符串fruit同名的常量時(shí),未加單引號(hào)的索引字符串輸出結(jié)果就成了carrot,而加上單引號(hào)還是apple。
結(jié)論:
1. 數(shù)組變量未用雙引號(hào)包括時(shí),
(1) 索引字符串加單引號(hào)表示字符串本身
pre name="code" class="php">$arr['fruit']
(2)索引字符串未加單引號(hào)表示常量,當(dāng)常量未定義時(shí)則解析為字符串,等效于加上單引號(hào)。
2. 數(shù)組變量用雙引號(hào)包括時(shí),
(1) 索引字符串不加單引號(hào)表示字符串本身
(2) 數(shù)組變量加上花括號(hào)表示與字符串同名常量
(3) 索引字符串加上單引號(hào)且數(shù)組變量加上花括號(hào)表示字符串本身
pre name="code" class="php">pre name="code" class="php">"{$arr['fruit']}"
(4) 索引字符串加上單引號(hào)且數(shù)組變量未加上花括號(hào),為錯(cuò)誤寫(xiě)法,報(bào)錯(cuò):Parse error: parse error, expecting T_STRING' or T_VARIABLE' or T_NUM_STRING'
pre name="code" class="php">pre name="code" class="php">"$arr['fruit']"
附:php手冊(cè)數(shù)組說(shuō)明URL
http://php.net/manual/zh/language.types.array.php
以上這篇基于php雙引號(hào)中訪(fǎng)問(wèn)數(shù)組元素報(bào)錯(cuò)的解決方法就是小編分享給大家的全部?jī)?nèi)容了,希望能給大家一個(gè)參考,也希望大家多多支持腳本之家。
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