9 common mistakes and tips that PHP programmers often make
When we have learned PHP for a period of time, we will develop certain bad habits. The following are 9 common mistakes compiled by the editor. For everyone to learn from.
1. Variable declaration
If you declare a variable in a statement, as follows: $var='value' ;The compiler first evaluates the right half of the statement, and it is this part of the statement that often causes errors. If you use incorrect syntax, you will get a parsing error.
2. Parse error
For example, Parse error: Parse error, unexpected T_WHILE in c:program filesapache groupapachehtdocsscript.php on line 19 Each time the previous error is determined , parsing errors keep appearing one after another, and PHP stops executing the script after the first parsing error. Also, parsing errors have very little information, with almost no reporting of the line number where the error occurred. For example, a predefined keyword is used in the expression, for example: while=10; while is a predefined keyword and cannot be assigned a value. Predefined keywords include while, function, etc. We cannot use these predefined keywords to name variables, otherwise the compiler will report an error. Among them, T_IF represents if(), T_WHILE represents while(), T_FOR represents for(), etc.
3. Common Errors
There are also some common errors, such as not ending the statement with a semicolon (;), missing quotation marks in the string, etc. In addition, if you do not use curly brackets (}) to end a function or a loop, for example: function UselessFunction(){for($i
4.MySQL error
Another type of error message is MySQL error, which often causes PHP novices to feel quite a headache, such as: Warning:Supplied argument is not a valid MySQL result resource in... The wrong line reported above may be: while($row=mysql_fetch_array($result)){}The parameter $result is not a valid resource, because the query fails and mysql_fetch_array cannot be processed. . If the syntax of any query is invalid or the connection to the database fails, you should go to the MySQL console for testing.
5. Pay attention to the difference between echo and print
Echo and print in PHP are both output functions, but there are still subtle differences between the two. There is no return value after echo output, but print has a return value, and it returns false when its execution fails. Therefore, it can be used as a normal function, for example, if $r=print "Hello World" is executed; the value of variable $r will be 1. Moreover, the echo statement in the code runs slightly faster than the print statement.
6. Pay attention to the difference between empty string ('') and NULL
Both empty strings and NULL in PHP are stored with a value of 0, but their The types are different. The former is string, while the latter is NULL. It can be seen that the string ('') and NULL values are equal but the types are different.
Distinguish the difference between == (equal) and === (all equal)
Both are comparison operators, == (equal) only compares whether the values are equal, and == = (all equals) not only compares whether the values are equal, but also compares whether the types are equal, which is more strict.
7. Distinguish the difference between include and require
The functions of include() and require() are basically the same, but there are some differences in usage, include() is a conditional inclusion function, while require() is an unconditional inclusion function. For example, in the following code, if the variable $a is true, the file a.php will be included: if($a){include("a.php");} and require() is different from include(), regardless of $ Whatever the value of a, the following code will include the file a.php: if($a){require("a.php");} In terms of error handling, use the include statement. If an inclusion error occurs, the program will skip include statement, although an error message will be displayed, the program will continue to execute. However, the require statement prompts a fatal error.
8. Pay attention to the difference between isset and empty
empty is to determine whether a variable is "empty", while isset is to determine whether a variable has been set.
9. Distinguish the difference between self:: and this-->
When accessing member variables or methods in a PHP class, if the referenced variable or If the method is declared as const (constant) or static (static attribute), you must use the domain operator::, and if the referenced variable or method is not declared as const or static, then use the pointer operator -> .
The above is the detailed content of 9 common mistakes and tips that PHP programmers often make. For more information, please follow other related articles on the PHP Chinese website!

What’s still popular is the ease of use, flexibility and a strong ecosystem. 1) Ease of use and simple syntax make it the first choice for beginners. 2) Closely integrated with web development, excellent interaction with HTTP requests and database. 3) The huge ecosystem provides a wealth of tools and libraries. 4) Active community and open source nature adapts them to new needs and technology trends.

PHP and Python are both high-level programming languages that are widely used in web development, data processing and automation tasks. 1.PHP is often used to build dynamic websites and content management systems, while Python is often used to build web frameworks and data science. 2.PHP uses echo to output content, Python uses print. 3. Both support object-oriented programming, but the syntax and keywords are different. 4. PHP supports weak type conversion, while Python is more stringent. 5. PHP performance optimization includes using OPcache and asynchronous programming, while Python uses cProfile and asynchronous programming.

PHP is mainly procedural programming, but also supports object-oriented programming (OOP); Python supports a variety of paradigms, including OOP, functional and procedural programming. PHP is suitable for web development, and Python is suitable for a variety of applications such as data analysis and machine learning.

PHP originated in 1994 and was developed by RasmusLerdorf. It was originally used to track website visitors and gradually evolved into a server-side scripting language and was widely used in web development. Python was developed by Guidovan Rossum in the late 1980s and was first released in 1991. It emphasizes code readability and simplicity, and is suitable for scientific computing, data analysis and other fields.

PHP is suitable for web development and rapid prototyping, and Python is suitable for data science and machine learning. 1.PHP is used for dynamic web development, with simple syntax and suitable for rapid development. 2. Python has concise syntax, is suitable for multiple fields, and has a strong library ecosystem.

PHP remains important in the modernization process because it supports a large number of websites and applications and adapts to development needs through frameworks. 1.PHP7 improves performance and introduces new features. 2. Modern frameworks such as Laravel, Symfony and CodeIgniter simplify development and improve code quality. 3. Performance optimization and best practices further improve application efficiency.

PHPhassignificantlyimpactedwebdevelopmentandextendsbeyondit.1)ItpowersmajorplatformslikeWordPressandexcelsindatabaseinteractions.2)PHP'sadaptabilityallowsittoscaleforlargeapplicationsusingframeworkslikeLaravel.3)Beyondweb,PHPisusedincommand-linescrip

PHP type prompts to improve code quality and readability. 1) Scalar type tips: Since PHP7.0, basic data types are allowed to be specified in function parameters, such as int, float, etc. 2) Return type prompt: Ensure the consistency of the function return value type. 3) Union type prompt: Since PHP8.0, multiple types are allowed to be specified in function parameters or return values. 4) Nullable type prompt: Allows to include null values and handle functions that may return null values.


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

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

SublimeText3 Linux new version
SublimeText3 Linux latest version

Dreamweaver Mac version
Visual web development tools

ZendStudio 13.5.1 Mac
Powerful PHP integrated development environment

SecLists
SecLists is the ultimate security tester's companion. It is a collection of various types of lists that are frequently used during security assessments, all in one place. SecLists helps make security testing more efficient and productive by conveniently providing all the lists a security tester might need. List types include usernames, passwords, URLs, fuzzing payloads, sensitive data patterns, web shells, and more. The tester can simply pull this repository onto a new test machine and he will have access to every type of list he needs.

SublimeText3 Mac version
God-level code editing software (SublimeText3)