Usage analysis of PHP composite data type array_PHP tutorial

For people, data type is a relatively difficult knowledge point to understand. In this article, we will explain how to use the PHP composite data type array in detail. We hope it will be helpful to everyone.

(1), array (array): The array in PHP actually uses an optimized ordered graph type as an array. Array indexes expressed as strings (except constants or variables) should always be enclosed in quotes.

PHP composite data type array definition array():

array( [key =>] // key can be integer or string
value // value can be any value
, ...
)

<ol class="dp-xml">
<li class="alt"><span><span class="tag"><span> ?php  </span></span></span></li>
<li>
<span>$</span><span class="attribute">arr</span><span> = </span><span class="attribute-value">array</span><span>("foo" =</span><span class="tag">></span><span> "bar", </span><span class="attribute">12</span><span> =</span><span class="tag">></span><span> true); //key如果是浮点数则取整为integer  </span>
</li>
<li class="alt"><span> </span></li>
<li><span>echo $arr["foo"]; // bar  </span></li>
<li class="alt"><span>echo $arr[12]; // 1  </span></li>
<li>
<span class="tag">?></span><span> </span>
</li>
</ol>

The default key name of PHP composite data type array takes the current largest integer index value, and the new key name index is the current largest The index is incremented by one. If the specified key name already has a value, the value will be overwritten. Since PHP 4.3.0, the above index generation method has changed. Now if you add a new value to an array whose current largest key is a negative value, the newly generated index will be zero (0). The previously newly generated index is the current maximum index plus one, which is the same as the positive index.

Add/modify array elements:

<ol class="dp-xml">
<li class="alt"><span><span class="tag"><span> ?php  </span></span></span></li>
<li>
<span>$</span><span class="attribute">arr</span><span> = </span><span class="attribute-value">array</span><span>(</span><span class="attribute">5</span><span> =</span><span class="tag">></span><span> 1, </span><span class="attribute">12</span><span> =</span><span class="tag">></span><span> 2);  </span>
</li>
<li class="alt"><span>$arr[] = 56; // This is the same as $arr[13] = 56;  </span></li>
<li><span>// at this point of the script  </span></li>
<li class="alt"><span>$arr["x"] = 42; // This adds a new element to  </span></li>
<li><span>// the array with key "x"  </span></li>
<li class="alt"><span>unset($arr[5]); // This removes the element from the array  </span></li>
<li><span>unset($arr); // This deletes the whole array  </span></li>
<li class="alt">
<span class="tag">?></span><span> </span>
</li>
</ol>

That’s it for the introduction of PHP composite data type array, I hope everyone can master this knowledge point.

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