PHP often uses dot styling, sprintf formatting, strpos search, str_replace replacement, trim cleaning, htmlspecialchars anti-XSS, and urlencode encoding. 1. Use . or sprintf() for splicing; 2. Use strpos() for search, and replace str_replace() for str_replace(); 3. Use trim(), strip_tags(), and htmlspecialchars() for cleaning; 4. Use mb_convert_encoding() for encoding and conversion, and use urlencode()/urldecode() for URL encoding and decoding.

It is actually very common to process strings in PHP, especially when doing web development, string operations are almost everywhere. Whether it is splicing URLs, filtering inputs, or generating dynamic content, it is inseparable from basic operations on strings. PHP provides a lot of built-in functions to help us process strings more efficiently.

Stitching and formatting strings

In PHP, the most common use of dot signs is the dot sign . Instead of using plus signs in some languages. for example:

 $name = "John";
$message = "Hello, " . $name . "! Welcome back.";

If you need clearer format control, consider using the sprintf() function, which is similar to printf in C, but does not output but returns a string. For example:

 $message = sprintf("Hello, %s! You have %d new messages.", $name, $count);

This method is more suitable for complex format combinations and is easier to maintain.

Small suggestions: If it is just a simple splicing, just use dot numbers; but if multiple variables are involved or a fixed format is required (such as amount, date, etc.), use sprintf() to make it clearer.

Find and replace substrings

Sometimes we need to determine whether there is a keyword in a string, or replace it with another word. At this time, you can use strpos() and str_replace() .

• strpos($haystack, $needle) is used to find the position (index) of $needle in $haystack . If it is not found, false will be returned.
• str_replace($search, $replace, $subject) can batch replace all matching content.

For example:

 $text = "This is a test string for testing.";
if (strpos($text, "test") !== false) {
    echo "Found the word 'test'.";
}

$newText = str_replace("test", "demo", $text);
// Output: This is a demo string for demoing.

Note: strpos() returns a position, not a Boolean value, so use !== false to determine whether it exists.

Clean and filter strings

User input often contains extra spaces or special characters, which needs to be cleaned up at this time. Commonly used functions are:

• trim() : Remove the blank spaces at both ends of the string (you can also specify the characters to be removed)
• htmlspecialchars() : prevents XSS attacks and escapes special characters into HTML entities
• strip_tags() : Remove HTML or PHP tags

For example, you got the username from the form:

 $input = " <b>John</b> ";
$clean = trim(strip_tags($input)); // Get "John"

If you want to display this username on the page, it is best to use htmlspecialchars() to prevent malicious script injection.

String encoding and conversion

Sometimes you will encounter Chinese garbled code or want to convert strings to lowercase/caps. Here are a few practical functions:

• strtolower() / strtoupper() : Convert case
• mb_convert_encoding() : used to handle conversion between different encodings (such as GBK to UTF-8)
• urlencode() / urldecode() : Safely transfer strings in URLs

For example, if you want to put Chinese as a parameter in the URL:

 $title = "Hello world";
$encoded = urlencode($title); // Output Hello World

In this way, after passing it over, and then solving it with urldecode() it can be restored to "Hello World".

Basically that's it. Although string operation is basic, using it skillfully can make the code more concise and safer, and can also avoid many common mistakes. If you master these directions well, daily development will basically be enough.

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