Home Backend Development PHP Tutorial Introduction to the role of braces in php_PHP tutorial

Introduction to the role of braces in php_PHP tutorial

Jul 21, 2016 pm 03:19 PM
for function name php one No What introduce effect brackets program

1. No matter what program, function name(){}, for(){}, ... there are too many, and you know what to do without even explaining them.
2. $str{4} is followed by {} after a string variable. Just like the curly brackets and square brackets, a certain string variable is treated as an array.
3. {$val} The role of the curly brackets at this time is to tell PHP that the enclosed items should be treated as variables.

Copy code The code is as follows:

$arr=array(0=>123, 'name'=>' Hello');
foreach($array as $k=>$v){
echo "select * from blog_blogs where blog_tags like '%{$arr[$k]}%' order by blog_id" ; //Adding a curly brace is just to use it as the identifier of the variable
}
echo '






';
foreach($array as $k=>$v){
echo "select * from blog_blogs where blog_tags like '%{{ $arr[$k]}}%' order by blog_id"; //Add two braces, the outer ones will be treated as ordinary characters
}
//Use braces to distinguish variables
/ /echo "$arr['name']"; //Using this sentence will report a syntax error
echo "{$arr['name']}"; //This sentence is normal, the characters in the braces will be used as variables To process
//$str{4} In the string variable followed by {} braces and square brackets, a string variable is treated as an array
$str = 'abcdefg';
echo $str{4};


{}The role of braces in php (the meaning of PHP variables placed inside braces)

For example: $sql = "insert into article (`channel_id`,`title`,`detail`,`pub_time`) values ​​('{$cid}','{$title}','{$detail}','{$ time}');";
It seems that it is OK without adding it. What does adding {} mean?
Why should the field name be included with ``?

===== =========================================

At least easy to read Well~~~'' is required by the insert into statement, because strings must appear in pairs
Adding {} is sometimes to prevent the variable name from being connected with the following string
For example,
{ $cid}dd
If cid=aa
then {$cid}dd=aadd
If you don’t add it, take a look at $ciddd yourself, wouldn’t it become a ciddd variable~~

Add a brace {} after the PHP variable and fill in the numbers, which refers to the characters of the corresponding serial number of the PHP variable.
For example:
$str = 'hello';
echo $str{0}; // The output is h
echo $str{1}; // The output is e
If you want To check whether a string meets a certain length, you can consider using braces (curly braces) plus isset to replace the strlen function. Because isset is a language structure and strlen is a function, using isset is more efficient than using strlen.
For example, to determine whether the length of a string is less than 5:
if ( !isset ( $str{5} ) ) is better than if ( strlen ( $str ) < 5 ).


The following explanations are more illustrative:

means that the variable inside {} is processed according to the variable during execution. The special method used to reference the variable in the string Include method, so you don't need to use the . operator, thus reducing the amount of code input.

In fact, the output block is equivalent to print "hello ".$arr['fruit'];

1. Variables using curly brackets
As mentioned in the previous blog, PHP Notice warns the following sentence:

switch (${action}.'_'.${child}) {
At first glance, there is no problem. I also checked the definition of variables in the PHP manual: here.
1. The situation of variable variables
It can be seen that, like most information, the use of braces for variables lies in "Variable variables". It is mentioned:


Quote
In order to use variable variables with arrays, you have to resolve an ambiguity problem. That is, if you write $$a[1] then the parser needs to know if you meant to use $a[1] as a variable, or if you wanted $$a as the variable and then the [1] index from that variable. The syntax for resolving this ambiguity is: ${$a[ 1]} for the first case and ${$a}[1] for the second.
In other words, in order to use variable variables in an array environment, it needs to be used appropriately according to different situations. Braces {} limit the scope of a variable. ${$a[1]} is completely different from ${$a}[1]:


Quote
${$a[1]} Here $a[1] is A variable;
${$a}[1] Here $a is a variable;
2. Delimit and avoid ambiguity
In fact, this situation is similar to that of variable variables. For example, if you use the "." connector to connect a string, it may look like this:

echo $str.'_2010';
Written in curly brackets, it may be simpler:

echo "${str}_2010";
It can be seen that if there are no curly brackets, $str_2010 may be processed as a variable. Of course, this way of writing can only be used within double quotes. Variable substitution will not be performed inside single quotes.

3. A single character in a string variable
For example:
Copy code The code is as follows:

$str='000';
$str{0}='1';
echo $str; //The output is 100
?> ;

This is not difficult to understand. It has the same effect as the square brackets []. It is somewhat similar to treating strings as objects in Python. Therefore, the following statements have the same function:
Copy the code The code is as follows:

$str= '000';
$str[0]='1';
echo $str; //also outputs 100
?>

However, these are not me What I want to explain, what I really want to describe, please see below.

2. Similarities and differences in using curly braces for variables
First, turn on all PHP error message output, that is, /etc/php.ini is:


Quote
error_reporting = E_ALL
display_errors = On
Then, open the test page, where the code is:
Copy the code The code is as follows:

$test='123';
echo $test;
echo "${test}";
echo "{$test}";
echo ${test}.'_';
echo ${test};
?>

You will see the following results:


Quote
123123123
Notice: Use of undefined constant test - assumed 'test' in /var/www/html/phpcrm/testpages/variables.php on line 6
123_
Notice: Use of undefined constant test - assumed 'test' in /var/www/html/phpcrm/testpages/variables.php on line 7
123
What does this mean?
1. Acceptable writing method
From the output result "123123123", it shows that the echo statements in the first three lines are normal:
Copy code The code is as follows:

echo $test;
echo "${test}";
echo "{$test}";

2 , Not recommended writing method
There are Notice warnings in the two lines after it, that is, the test variable was regarded as a constant, but it was later assumed to be a variable. Therefore, in order to avoid ambiguity and conflicts, it is not recommended to write like this:
Copy code The code is as follows:

echo ${test} .'_';
echo ${test};

However, there is an alternative way of writing
Copy code The code is as follows:

echo ${'test'}.'_';
echo ${'test'};

Writing like this will not An error will be reported
3. Incorrect writing
According to many information on the Internet, ${var} and {$var} have the same effect. However, if you add another sentence:

echo {$test};
then you will get the following error message:


Quote
Parse error: syntax error, unexpected '{' in /var/www/html/phpcrm/testpages/variables.php on line 8
This is not a Notice warning, but an error. Due to parsing problems, the program will not run normally.

3. Summary
Combining the contents of the previous two parts, I believe that the following principles should be followed when using curly braces for variable references:


Quotation
1. The correct way to write it is: in the form of ${var};
2. Use it with double quotes;
3. Delimit it according to the meaning to be expressed.
So, finally I changed the switch line to:

switch ("${action}_${child}") {
That is, the Notice warning will no longer appear.

www.bkjia.comtruehttp: //www.bkjia.com/PHPjc/325229.htmlTechArticle1. No matter what program, function name(){}, for(){}, .... too many , even if you don’t say it, you know what to do. 2. $str{4} is followed by {} braces and square brackets after the string variable...
Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

Video Face Swap

Video Face Swap

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

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

Hot Topics

Java Tutorial
1664
14
PHP Tutorial
1268
29
C# Tutorial
1242
24
Explain JSON Web Tokens (JWT) and their use case in PHP APIs. Explain JSON Web Tokens (JWT) and their use case in PHP APIs. Apr 05, 2025 am 12:04 AM

JWT is an open standard based on JSON, used to securely transmit information between parties, mainly for identity authentication and information exchange. 1. JWT consists of three parts: Header, Payload and Signature. 2. The working principle of JWT includes three steps: generating JWT, verifying JWT and parsing Payload. 3. When using JWT for authentication in PHP, JWT can be generated and verified, and user role and permission information can be included in advanced usage. 4. Common errors include signature verification failure, token expiration, and payload oversized. Debugging skills include using debugging tools and logging. 5. Performance optimization and best practices include using appropriate signature algorithms, setting validity periods reasonably,

Explain late static binding in PHP (static::). Explain late static binding in PHP (static::). Apr 03, 2025 am 12:04 AM

Static binding (static::) implements late static binding (LSB) in PHP, allowing calling classes to be referenced in static contexts rather than defining classes. 1) The parsing process is performed at runtime, 2) Look up the call class in the inheritance relationship, 3) It may bring performance overhead.

What are PHP magic methods (__construct, __destruct, __call, __get, __set, etc.) and provide use cases? What are PHP magic methods (__construct, __destruct, __call, __get, __set, etc.) and provide use cases? Apr 03, 2025 am 12:03 AM

What are the magic methods of PHP? PHP's magic methods include: 1.\_\_construct, used to initialize objects; 2.\_\_destruct, used to clean up resources; 3.\_\_call, handle non-existent method calls; 4.\_\_get, implement dynamic attribute access; 5.\_\_set, implement dynamic attribute settings. These methods are automatically called in certain situations, improving code flexibility and efficiency.

PHP and Python: Comparing Two Popular Programming Languages PHP and Python: Comparing Two Popular Programming Languages Apr 14, 2025 am 12:13 AM

PHP and Python each have their own advantages, and choose according to project requirements. 1.PHP is suitable for web development, especially for rapid development and maintenance of websites. 2. Python is suitable for data science, machine learning and artificial intelligence, with concise syntax and suitable for beginners.

PHP in Action: Real-World Examples and Applications PHP in Action: Real-World Examples and Applications Apr 14, 2025 am 12:19 AM

PHP is widely used in e-commerce, content management systems and API development. 1) E-commerce: used for shopping cart function and payment processing. 2) Content management system: used for dynamic content generation and user management. 3) API development: used for RESTful API development and API security. Through performance optimization and best practices, the efficiency and maintainability of PHP applications are improved.

PHP: A Key Language for Web Development PHP: A Key Language for Web Development Apr 13, 2025 am 12:08 AM

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 Enduring Relevance of PHP: Is It Still Alive? The Enduring Relevance of PHP: Is It Still Alive? Apr 14, 2025 am 12:12 AM

PHP is still dynamic and still occupies an important position in the field of modern programming. 1) PHP's simplicity and powerful community support make it widely used in web development; 2) Its flexibility and stability make it outstanding in handling web forms, database operations and file processing; 3) PHP is constantly evolving and optimizing, suitable for beginners and experienced developers.

Explain the match expression (PHP 8 ) and how it differs from switch. Explain the match expression (PHP 8 ) and how it differs from switch. Apr 06, 2025 am 12:03 AM

In PHP8, match expressions are a new control structure that returns different results based on the value of the expression. 1) It is similar to a switch statement, but returns a value instead of an execution statement block. 2) The match expression is strictly compared (===), which improves security. 3) It avoids possible break omissions in switch statements and enhances the simplicity and readability of the code.

See all articles