5 common questions among junior PHP developers

1. What details should be paid attention to when uploading files? How to save files to a specified directory? How to avoid the problem of uploading files with duplicate names?

1). First, you need to enable file upload in php.ini;

2). There is a maximum allowed upload value in php.ini, the default is 2MB. It can be changed when necessary;

3). When uploading the form, be sure to write enctype="multipart/form-data" in the form tag;

4). Submission method is required It is a post;

5). Set the form control with type="file" and must have a name attribute value;

6). In order to upload successfully, you must ensure that the size of the uploaded file is correct Exceeds the standard, whether the file type meets the requirements, and whether the path where it is stored after uploading exists;

7). The form is submitted to the receiving page, and the receiving page uses $_FILES to receive the uploaded files. $_FILES is a multidimensional array.

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

respectively represent the file name, file type, temporary file name uploaded to the temporary directory, file size, and whether there are errors.

If it is a batch upload, then the two-dimensional subscript is an array, not a string.

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

9). In order to avoid uploading files with duplicate names, you can get the file suffix from the uploaded file name, and then rename the file using the timestamp + file suffix.

2. The relationship and difference between $_REQUEST, $_GET, $_POST, and $_COOKIE:

1. Relationship: $_REQUEST includes $_GET, $_POST, $_COOKIE All contents are a collection of them.
   

2. $_GET, $_POST, $_COOKIE all have a copy in $_REQUEST. Changing the value of $_REQUEST does not affect $_GET etc. and vice versa.
   

3. When GET and POST have the same name, $_REQUEST takes the value of POST. When COOKIE has the same name as GET or POST, $_REQUEST takes the value of COOKIE. COOKIE has the highest priority. mistake.

3. What is SQL injection? How to prevent SQL injection?

SQL injection attack is one of the common means used by hackers to attack databases. Some programmers

do not judge the legality of user input data when writing code. The injector can enter a database query code in the form and submit it, and

the program will submit it. The information is pieced together to generate a complete SQL statement, and the server is tricked into executing the malicious SQL command. Based on the results returned by the program, the injector successfully obtains some sensitive data and even controls the entire server. This is SQL injection.

To filter the submitted information, escape the single quotes.

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

4. What is the concept of MVC?

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

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

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

The purpose of the existence 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 updated synchronously.

Separate M and V, you can make the same web page display different page styles when different holidays come. This only requires making multiple view layer template pages in advance,

Without changing the M layer program.

MVC achieves division of labor and cooperation in programming, maximizing code reusability, making program logic clearer and more organized, and facilitating later maintenance and management.

In website development,

The model layer is generally responsible for adding, deleting, modifying, and checking database table information,

The view layer is responsible for displaying page content, and

control The controller layer plays a regulating role between M and V. The controller layer decides which method of which model class to call.

After the execution is completed, the controller layer decides which view layer to assign the result to.

5. What do $this, self and parent represent respectively? When to use

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

Usage occasions:

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

self can only be used in the current class, and can be accessed in the current class through the scope operator:: Class constants, static properties in the current class, methods in the current class;

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

Usage scenarios for operators

a) In this class:

i.self::Class constant

ii.self::static Attribute

iii.self::Method() parent::Method()

b) In subclass:

i.parent::Class constant

ii.parent::Static property (public or protected)

iii.parent::Method () (public or protected)

c) Outside the class:

i.Class name::Class constant

ii. Class name:: Static property (public)

iii. Class name:: Static method (public)