Shulou(Shulou.com)06/02 Report--

In this issue, the editor will bring you five common questions about PHP junior developers. The article is rich in content and analyzed and described from a professional point of view. I hope you can get something after reading this article.

What details should I pay attention to when uploading files? How to save the file to the specified directory? How to avoid the problem of uploading files with duplicate names?

1)。 First of all, you need to enable file upload in php.ini.

2)。 There is a maximum allowed upload in php.ini, and the default is 2MB. Can be changed if necessary

3)。 When uploading a form, remember to write enctype= "multipart/form-data" in the form tag.

4)。 Submission method method must be post

5)。 Set the form control for type= "file" and must have the value of the name property

6)。 In order to upload successfully, we must ensure whether the size of the uploaded file exceeds the standard, whether the file type meets the requirements, and whether the path to be stored after upload exists.

7)。 The form is submitted to the receiving page, which uses $_ FILES to receive the uploaded file. $_ FILES is a multidimensional array.

The first subscript is the name of the upload control, and the two-dimensional subscript is name/type/tmp_name/size/error.

Represents the file name, file type, temporary file name uploaded to the temporary directory, file size, whether there is an error.

If it is a batch upload, then the 2D subscript is an array, not a string.

8)。 After the file is uploaded, it is placed under the server-side temporary path. You need to use the move_uploaded_file () function to save the uploaded file to the specified directory.

9)。 To avoid uploading a file with the same name, you can get the file suffix from the uploaded file name, and then rename the file using a timestamp + file suffix.

Second, the relationship and difference between $_ REQUEST, $_ GET, $_ POST and $_ COOKIE:

1. Relationship: $_ REQUEST contains all the contents of $_ GET, $_ POST, $_ COOKIE, etc., and is a collection of them.

two。 Get the value of the variable through $_ REQUEST, because the PHP page is not sure which way to pass the value

Therefore, the value is received according to the configuration in php.ini.

It can be set in php.ini, variables_order = "GPC". It means GET,POST,COOKIE.

So the PHP page is first obtained from $_ GET, then from $_ POST, and then from $_ COOKIE.

The newly obtained value overrides the previously obtained value.

So in terms of representation, $_ REQUEST ends up getting the value in $_ COOKIE, if there is no value in $_ COOKIE

Gets the value in $_ POST, and if $_ POST doesn't get it, go to $_ GET to get it.

If there is no such value in $_ GET, then $_ REQUEST returns null.

What is SQL injection? How to prevent SQL injection?

SQL injection attack is one of the common means for hackers to attack database. When some programmers write code,

Without judging the validity of the data entered by the user, the injector can enter a database query code into the form and submit it.

The program pieced together the submitted information to generate a complete sql statement, and the server was deceived into executing the malicious SQL command. The result returned by the injector according to the program

Successful access to some sensitive data and even control of the entire server is called SQL injection.

To filter the submitted information and escape the single quotation marks.

You can first set it in php.ini so that all single quotes are escaped after submission. Or use addslashes ().

What is the concept of MVC?

MVC (Model-View-Controller) is a kind of software design pattern or programming idea invented in 1980s.

M refers to (Model) model layer, V refers to (View) view layer (display layer or user interface), and C refers to (Controller) control layer.

The purpose of using mvc is to achieve the separation of M and V, so that a program can easily use different user interfaces.

The purpose of C is to play a regulating role between M and V to ensure the synchronization of M and V. once M changes, V should be able to update synchronously.

By separating M and V, we can achieve the same web page and display different page styles when different festivals come. it only needs to make multiple view layer template pages in advance.

There is no need to change the M layer program.

MVC achieves the division of labor and cooperation in programming, the reusability of the code is maximized, and the program logic is more clear and organized, which is convenient for later maintenance and management.

In the development of the website

The model layer is generally responsible for adding, deleting, modifying and querying the database table information.

The view layer is responsible for displaying the page content.

The controller layer acts as a moderator between M and V, and the controller layer decides which method of which model class is called.

After execution, it is up to the controller layer to decide which view layer to assign the result to.

5. What do $this,self and parent stand for respectively? On what occasions do you use it?

$this represents the current object self represents the current class parent represents the parent class of the current class

Where to use:

$this can only be used in the current class, and properties and methods in the current class can be called through $this- >

Self can only be used in the current class, through the scope operator:: access class constants in the current class, static properties in the current class, and methods in the current class

Parent can only be used in the current class that has a parent class, through the scope operator:: access to class constants in the parent class, static properties in the parent class, and methods in the parent class.

Act on the use of operators

A) in this category:

I.selfpurl: class constant

Ii.self:: static property

Iii.self:: method () parent:: method ()

B) in subclass:

I.parentPlux: class constant

Ii.parent:: static property (public or protected)

Iii.parent:: method () (public or protected)

C) out of category:

i. Class name:: class constant

ii. Class name: static property (public)

iii. Class name:: static method (public)

These are the five common questions shared by the editor for junior developers of PHP. If you happen to have similar questions, please refer to the above analysis to understand. If you want to know more about it, you are welcome to follow the industry information channel.

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