PHP Learning String Comparison and Search_PHP Tutorial
1. String comparison
In PHP, you can use == (double equal sign) or === (triple equal sign) to compare strings. The difference between the two is that the double equal sign does not compare types, while the triple equal sign will compare types, but does not convert types; when comparing with a double equal sign, if there is a numeric value on the left and right sides of the equal sign, the other value will be converted as a number and then compare. In this case, if it is a pure string or NULL, it will be converted to 0 for comparison. Similarly, the greater than or equal sign is the same as the equal sign, and incorrect results may occur during comparison.
So, you can use PHP’s built-in functions strcmp and strcasecmp to compare strings. Among them, strcasecmp is a variant of strcmp. It converts the string to lowercase first and then compares it. The following code:
var_dump(0 == 'Test');
var_dump( 0 == '');
var_dump(5 > 'T');
var_dump(strcmp(5, 'T'));
The result is (1st~ 3 results are incorrect, only the 4th one is correct):
bool(true )
bool(true)
bool(true)
int(-1)
2. String processing
1. Substring
$sub = substr(string, start[, length]);
2. Substring replacement
$newstring = substr_replace(string, new, start[, length]);
Use this function String insertion and deletion operations can be implemented. The start and length of this function can be negative numbers. Respectively means counting from the end and retaining the last few digits without replacement. ３. String reverse order
$newstring = strrev(string);
４. Repeat string
$newstring = str_repeat(string, count);
Return a new character that repeats count times string string.
５. Filling string
$newstring = str_pad(to_pad, length[, with[, type]]);
There are three types of types: STR_PAD_RIGHT (default), STR_PAD_LEFT and STR_PAD_BOTH; with default is Space. The function indicates that the to_pad string is filled with with into a string with a length of length. The following code:
// Substring
var_dump(substr('1234567890', 8)); // 90
var_dump(substr('1234567890', 0, 2)); // 12
// Reverse substring
var_dump(substr('1234567890', -8) ); // 34567890
var_dump(substr('1234567890', -8, -2)); // 345678
var_dump(substr('1234567890', -8, 2)); // 34
//Insert
var_dump(substr_replace('1234567890', 'a', 0, 0)); // a1234567890
// Delete
var_dump(substr_replace('1234567890', '', 8) ; ('1234567890', 'a', 0, 1)); // a234567890
// Replace in the opposite direction
var_dump(substr_replace('1234567890', 'a', -2, -1)); / / 12345678a0
// String reverse
var_dump(strrev('1234567890')); // 0987654321
// Repeat string
var_dump(str_repeat('12', 3)); // 121212
// Filling string
var_dump(str_pad('a', 10, '12')); // a121212121
var_dump(str_pad('a', 10, '12', STR_PAD_LEFT)); // 121212121a
var_dump(str_pad('a', 10, '12', STR_PAD_BOTH)); // 1212a12121
3. Decompose string
When strtok is marked, use strtok($str, $token) to initialize, and use strtok($token) to continue to obtain the value. The code is as follows:
Copy code
$str2 = strtok($str, ' ,'); // 1
$str3 = strtok(','); // 2
$str4 = strtok(','); // 3
// array(86, 10, 88888888, 'Beijin')
$arr3 = sscanf('+86(10)88888888 Beijin', '+%d(%d)%d %s');
4. String search
In PHP, there are three series of string search. Returns the position, returns the string, and matches the number of masks. Among them, there are two functions that return positions, strpos() and strrpos(); there are also two functions that return strings, strstr() and strchr(); functions that return mask matching numbers include strspn() and strcspn() .
strpos means counting from the left and returns the position where the string to be found first appears; strrpos means counting from the right and returns the position where the string to be found first appears.
strstr means counting from the left and returns the substring from the first to the end of the string to be searched (including the search string). When searching for characters, you can use ASCII code numbers to represent characters; strstr means not to distinguish between sizes Search; strchr is an alias of strstr; strrchr returns the substring from the last occurrence of the character to the end.
strspn means counting from the left, the number of characters of the substring before the first non-masked occurrence; strcspn means counting from the left, the number of characters of the substring before the first occurrence of the mask.
Sample code:
$pos = strpos('This a hello world program' , ' '); // 4
$pos = strpos('This a hello world program', 32); // 4
$pos = strrpos('This a hello world program', ' '); // 18
$pos = strrpos('This a hello world program', 32); // 18
$str = strstr('This a hello world program', ' '); // " a hello world program"
$str = strstr('This a hello world program', 32); // " a hello world program"
$str = stristr('This a hello world program', ' A') ; // "a hello world program"
$str = stristr('This a hello world program', 65); // "a hello world program"
$str = strrchr('This a hello world program', 65); // "a hello world program"
$str = strrchr('This a hello world program', 65); ', ' '); // " program"
$str = strrchr('This a hello world program', 32); // " program"
$str1 = "12345 12345 12345";
$len = strspn($str1, '12345'); // 5
$len = strcspn($str1, ' '); // 5
Reference: PHP Programming, 2003, Chapter 4 Strings, String Comparison; String Search and Processing
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
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
1664
14
1423
52
1318
25
1269
29
1248
24
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::).
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?
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
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
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
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?
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.
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.
