array_key_exists()函数判断某个数组中是否存在指定的key,如果key存在,则返回true,否则返回flase
array_key_exists(key,array);
key:必需。规定键名
array:必需。规定输入的数组
<?php $a = array('a'=>'Dog','b'=>'Cat'); if(array_key_exists('a',$a)){ echo 'Key exists!'; } else{ echo 'Key does not exist!'; } ?>
输出:Key exists!
array_key_exists为什么比in_array快?
array_key_exists 和 in_array 查询的东西都不一样吧
array_key_exists 判断是否有键值
array_key_exists(a,arr)->if(isset(arr[a]))就是true
而in_array 需要去遍历值 遍历到了才跳出循环
追问:
是不是数组的索引有单独的存储单元,而且优化过,array_key_exists的时间复杂度是o(1), 而in_array是o(n) ??
追答:
重复杂度来说是这样
array_key_exists 是判断某个键有没有值
in_array 要遍历一次 获取是否相同 不知道建的情况下必须遍历
PHP中isset与array_key_exists的区别
1.对于数组值的判断不同,对于值为null或''或false,isset返回false,array_key_exists返回true;
2. 执行效率不同,isset是内建运算符,array_key_exists是php内置函数,isset要快一些。请参考:PHP 函数实现原理及性能分析
3.当用isset访问一个不存在索引数组值时,不会引起一个E_NOTICE的php错误消息;
4.array_key_exists 会调用get_defined_vars判断数组变量是否存在,isset不用;
测试代码:
<?php function microtime_float() { list($usec, $sec) = explode(" ", microtime()); return ((float)$usec + (float)$sec); } $test_arr['aa']='dd'; $test_arr['bb']=''; $test_arr['cc']=NULL; $test_arr['dd']=false; $test_arr= array('aa'=>'dd','bb'=>'','cc'=>null,'dd'=>false); echo "isset aa is ";var_dump(isset($test_arr['aa']));echo "n"; echo "isset bb is ";var_dump(isset($test_arr['bb']));echo "n"; echo "isset cc is ";var_dump(isset($test_arr['cc']));echo "n"; echo "isset dd is ";var_dump(isset($test_arr['cc']));echo "n"; echo "isset none is ";var_dump(isset($test_arr['none']));echo "n"; echo "key_exist aa is ";var_dump(array_key_exists('aa',$test_arr));echo "n"; echo "key_exist bb is ";var_dump(array_key_exists('bb',$test_arr));echo "n"; echo "key_exist cc is ";var_dump(array_key_exists('cc',$test_arr));echo "n"; echo "key_exist dd is ";var_dump(array_key_exists('dd',$test_arr));echo "n"; echo "key_exist none is ";var_dump(array_key_exists('none',$test_arr));echo "n"; $time_start = microtime_float(); for($i=0;$i<100;$i++){ isset($test_arr['aa']); } $time_end = microtime_float(); $time = $time_end - $time_start; echo "isset 100 is $timen"; for($i=0;$i<10000;$i++){ isset($test_arr['aa']); } $time_end = microtime_float(); $time = $time_end - $time_start; echo "isset 10000 is $timen"; for($i=0;$i<1000000;$i++){ isset($test_arr['aa']); } $time_end = microtime_float(); $time = $time_end - $time_start; echo "isset 1000000 is $timen"; //++++++++++++++++++++++++++++++ $time_start = microtime_float(); for($i=0;$i<100;$i++){ array_key_exists('aa',$test_arr); } $time_end = microtime_float(); $time = $time_end - $time_start; echo "array_key_exists 100 is $timen"; for($i=0;$i<10000;$i++){ array_key_exists('aa',$test_arr); } $time_end = microtime_float(); $time = $time_end - $time_start; echo "array_key_exists 10000 is $timen"; for($i=0;$i<1000000;$i++){ array_key_exists('aa',$test_arr); } $time_end = microtime_float(); $time = $time_end - $time_start; echo "array_key_exists 1000000 is $timen";

PHP remains important in modern web development, especially in content management and e-commerce platforms. 1) PHP has a rich ecosystem and strong framework support, such as Laravel and Symfony. 2) Performance optimization can be achieved through OPcache and Nginx. 3) PHP8.0 introduces JIT compiler to improve performance. 4) Cloud-native applications are deployed through Docker and Kubernetes to improve flexibility and scalability.

PHP is suitable for web development, especially in rapid development and processing dynamic content, but is not good at data science and enterprise-level applications. Compared with Python, PHP has more advantages in web development, but is not as good as Python in the field of data science; compared with Java, PHP performs worse in enterprise-level applications, but is more flexible in web development; compared with JavaScript, PHP is more concise in back-end development, but is not as good as JavaScript in front-end development.

PHP and Python each have their own advantages and are suitable for different scenarios. 1.PHP is suitable for web development and provides built-in web servers and rich function libraries. 2. Python is suitable for data science and machine learning, with concise syntax and a powerful standard library. When choosing, it should be decided based on project requirements.

PHP is a scripting language widely used on the server side, especially suitable for web development. 1.PHP can embed HTML, process HTTP requests and responses, and supports a variety of databases. 2.PHP is used to generate dynamic web content, process form data, access databases, etc., with strong community support and open source resources. 3. PHP is an interpreted language, and the execution process includes lexical analysis, grammatical analysis, compilation and execution. 4.PHP can be combined with MySQL for advanced applications such as user registration systems. 5. When debugging PHP, you can use functions such as error_reporting() and var_dump(). 6. Optimize PHP code to use caching mechanisms, optimize database queries and use built-in functions. 7

The reasons why PHP is the preferred technology stack for many websites include its ease of use, strong community support, and widespread use. 1) Easy to learn and use, suitable for beginners. 2) Have a huge developer community and rich resources. 3) Widely used in WordPress, Drupal and other platforms. 4) Integrate tightly with web servers to simplify development deployment.

PHP remains a powerful and widely used tool in modern programming, especially in the field of web development. 1) PHP is easy to use and seamlessly integrated with databases, and is the first choice for many developers. 2) It supports dynamic content generation and object-oriented programming, suitable for quickly creating and maintaining websites. 3) PHP's performance can be improved by caching and optimizing database queries, and its extensive community and rich ecosystem make it still important in today's technology stack.

In PHP, weak references are implemented through the WeakReference class and will not prevent the garbage collector from reclaiming objects. Weak references are suitable for scenarios such as caching systems and event listeners. It should be noted that it cannot guarantee the survival of objects and that garbage collection may be delayed.

The \_\_invoke method allows objects to be called like functions. 1. Define the \_\_invoke method so that the object can be called. 2. When using the $obj(...) syntax, PHP will execute the \_\_invoke method. 3. Suitable for scenarios such as logging and calculator, improving code flexibility and readability.


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

AI Hentai Generator
Generate AI Hentai for free.

Hot Article

Hot Tools

Atom editor mac version download
The most popular open source editor

SAP NetWeaver Server Adapter for Eclipse
Integrate Eclipse with SAP NetWeaver application server.

PhpStorm Mac version
The latest (2018.2.1) professional PHP integrated development tool

Dreamweaver CS6
Visual web development tools

mPDF
mPDF is a PHP library that can generate PDF files from UTF-8 encoded HTML. The original author, Ian Back, wrote mPDF to output PDF files "on the fly" from his website and handle different languages. It is slower than original scripts like HTML2FPDF and produces larger files when using Unicode fonts, but supports CSS styles etc. and has a lot of enhancements. Supports almost all languages, including RTL (Arabic and Hebrew) and CJK (Chinese, Japanese and Korean). Supports nested block-level elements (such as P, DIV),