Summary of the latest classic PHP interview questions (Part 1)

This article mainly introduces the latest summary of PHP classic interview questions in 2017 (Part 1). It is very good and has reference value. Friends in need can refer to it

##1. The difference between double quotes and single quotes

• Double quotes interpret variables, single quotes do not interpret variables

• In double quotes Insert single quotes. If there is a variable in the single quotes, the variable explanation

• The double quotes

  variable name must be followed by a non-number, letter, or underscore. Special characters, or use {} to enclose the variable, otherwise the part after the variable name will be treated as a whole, causing grammar errors

• Double quotes interpret escape characters, single quotes do not interpret escape characters, but interpreting '\ and \\

• can make single quote characters use single quotes as much as possible. Single quotes are more efficient than Double quotation marks should be taller (because double quotation marks must be traversed first to determine whether there are variables inside, and then operated, while single quotation marks do not need to be judged)

2. Commonly used superglobal variables(8)

##$_GET ----->get transmission method
$POST ----->post transmission method
$REQUEST ----->Can receive both get and post The value of the method
***
$GLOBALS ----->All variables are placed inside
$FILE ----->Upload files using
$SERVER ----->System environment variables
* **
$SESSION ----->Will be used during session control
$ COOKIE ----->It will be used for session control

3. The difference between POST, GET, PUT and DELETE methods in HTTP HTTP defines different methods of interacting with the server. The most basic ones are POST, GET, PUT, and DELETE. The full name of the indispensable URL is resource descriptor. We can understand it like this: URL describes a resource on the Internet, and post, get, put, and delegate are operations to add, delete, modify, and check this resource!

3.1 The difference between get and post submission methods in the form

get adds the parameter data queue to the submission form In the URL pointed to by the action attribute, the value corresponds one-to-one with each field in the form, which can be seen from the URL; post uses the HTTPPOST mechanism to prevent each field in the form and its content from being transmitted to the action attribute in the HTML head. Referring to the url address, the user cannot see this process
For the get method, the server side uses Request.QueryString to obtain the value of the variable. For the post method, the server side uses Request.Form to obtain it. Submitted data
get transfers a smaller amount of data, while post transfers a larger amount of data. It is generally unrestricted by default, but in theory, the maximum amount in IIS4 is 80kb. In IIS5 it is 1000k,
get security is very low, post security is high

• 
  

3.2

The GET request will send a request for data to the database to obtain information. This request is just like the select operation of the database. It is only used to
• query

  the data and will not be modified or added. The data will not affect the content of the resource, that is, the request will have no side effects. No matter how many times you perform the operation, the result is the same.

Different from GET, the PUT request sends data to the server to change the information. This request is just like the update operation of the database, used to modify the content of the data, but The types of data will not be increased, which means that no matter how many PUT operations are performed, the results will not be different.
• POST request

  is similar to PUT request, both send data to the server, but this request will change the type of data and other resources, just like the insert of the database The operation is the same, new content will be created. Almost all current submission operations are requested using POST.

DELETE request, as the name suggests, is used to delete a certain resource. This request is like the
• delete operation

  of the database.

4. Introduction to PHPHypertext Preprocessor----Hypertext Preprocessor

Personal Home Page Original name

Target purpose: Allow web developers to quickly write dynamically generated web pages. Compared with other pages, PHP embeds the program into the

HTML document

for execution. , much more efficient than CGI that completely generates HTML editingHTML: Hypertext Markup Language

Founder: Rasmus Lerdorf, born in 1968, University of Waterloo, Canada

Ledolf ​​initially wrote the maintenance program in prel language in order to maintain his personal web page, and then rewritten it in c, which eventually led to php/fi

Timeline:

• 1995.06.08 PHP/FI will be released to the public

• 1995 php2.0, adding support for MySQL

• 1997 php3.0

• 2000 php4.0

• 2008 php5.0

• Since php6.0 does not completely solve Unicode encoding, there are basically no applications on the production line. It is basically just a concept product. Many functions have been implemented on php5.3.3 and php5.3.4

• Common IDE(Intergrated Development Environment): Integrated Development Environment

Coda (mac)
PHPStrom
Adobe Dreamweaver
NetBeans

Common textEditor, with code highlighting:

NodePad++
SublimeText

PHP Advantages

PHP features:

• php uniquely mixes C, Java, Prel and PHP’s own syntax
  

• Can execute dynamic web pages faster than CGI or Prel. Compared with other programming languages, PHP embeds programs into HTML documents for execution, and its execution efficiency is higher than CGI that completely generates HTML editing. Much higher, all CGI can be implemented
  

• Supports almost all popular databases and operating systems
  

• PHP can Use C, C++ to extend the program
  

##Advantages of PHP:

• Open source code

• Free sex

• Quickness

• Cross-platform strong

• High efficiency

• Graphics processing

• Object-oriented

• Professional focus

  
  

PHP technology application:

• Static page generation

• Database cache

• Process cache

• p+css

  w3cStandard

• Big Load

• Distributed

• flex

• Support

  MVC

• Smarty Module Engine

  
  

##PHP Certification Level

Junior IFE: Index Front Engineer Front-end Engineer

Intermediate IPE: Index PHP Engineer PHP Engineer

Senior IAE: Index Architecture Engineer Architecture Engineer

6, echo, print_r, The difference between print and var_dump

* echo、print是php语句，var_dump和print_r是函数
* echo 输出一个或多个字符串，中间以逗号隔开，没有返回值是语言结构而不是真正的函数，因此不能作为表达式的一部分使用
* print也是php的一个关键字，有返回值 只能打印出简单类型变量的值(如int，string)，如果字符串显示成功则返回true，否则返回false
* print_r 可以打印出复杂类型变量的值(如数组、对象）以列表的形式显示，并以array、object开头，但print_r输出布尔值和NULL的结果没有意义，因为都是打印"\n"，因此var_dump()函数更适合调试
* var_dump() 判断一个变量的类型和长度，并输出变量的数值

7、HTTP status codeClick Check out the detailed explanation of HTTP status codes here

Common HTTP status codes:

200 - Request successful

301 - The resource (web page, etc.) is permanently escaped to other URL

404 - The requested resource (web page, etc.) does not exist
505 - Internal server error
HTTP status code classification:

1** - Information, the request received by the server requires the requester to continue performing the operation

2** - Success, the operation was successfully received and processed

3** - Redirect, further action is required to complete the request
4** - Client error, the request contained a syntax error or the request could not be completed
5** Server error, an error occurred while the server was processing the request

8. What are magic quotesMagic quotes are a process that will automatically escape the data entering the PHP script. It is best not to escape when encoding but to escape as needed during runtime

9. How to obtain the client's IP (requires an int) and the code of the server's IP##Client: $_SERVER["REMOTE_ADDR"]; or getenv('REMOTE_ADDR')ip2long for conversion

Server side: gethostbyname('www.baidu.com')

##10. Use those tools for version control

cvs, svn, vss, git

11. Methods to optimize the database

MySQL databaseEight ways to optimize (classic must-see) Click to get

Select the most applicable field attributes, reduce the width of the defined fields as much as possible, and try to set the fields to NOTNULL, such as ' It is best to use ENUM for province' and 'gender'Use connection (JOIN) instead of subqueryUse union (UNION) instead of manually created temporary table

Transaction processing

Lock table and optimize transaction Processing
Apply foreign keys, optimize locked tables
Establish indexes
Optimize query statements

12. Have you ever used template engine? What is the name of the template engine used?

Smarty: Smarty is a very old PHP template engine. It was my initial choice for using templates in this language. Although it is updated less frequently and lacks some features of the new generation of template engines, it is still worth a look.

13. For high-traffic websites, what methods should be used to solve the traffic problem

Confirm whether the server hardware can support the current traffic
Separate reading and writing of database, optimize data tables
Program function rules, prohibit external hot links
Control the download of large files
Use different hosts to divert main traffic

14. What is the difference between statements include and require? To avoid including the same file multiple times, you can use (?) statements to replace them

require is an unconditional inclusion, that is, if require is added to a process, it will be executed first regardless of whether the condition is true or not. require, when the file does not exist or cannot be opened, an error will be prompted and the program execution will be terminated

include has a return value, but require does not (probably because require is faster than include), if it is included If the file does not exist, an error will be prompted, but the program will continue to execute

Note: Included filerequire is fatal when it does not exist or has a syntax error, but include is not

require_once indicates that it is included only once, avoiding repeated inclusion

15. Talk about the understanding of mvc

The application is completed by the model, view, and controller. The model sends the functions to be implemented to the controller, and the controller receives the organizational functions and passes them to the view

16. Explain the difference between passing by value and passing by reference in PHP, and explain when passing by reference when passing by value?

Variables are always assigned by value by default, that is to say, when the value of an expression is assigned to a variable, the value of the entire expression is assigned to the target variable, which means Note: When one variable is assigned to another variable, changing the value of one variable will not affect the other variable

php also provides another way to assign values ​​to variables: reference assignment. This means that the new variable simply references (in other words, becomes an alias or points to) the original variable. Changes to new variables will affect the original variables and vice versa. Using reference assignment, simply add an & symbol before the variable to be assigned (source variable)

The object defaults to pass-by-reference

For larger data, it is better to pass-by-reference. This can save memory overhead

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