String Functions

Official PHP Documentation:

• PHP String Functions ↗

String Length and Character Access

String Length

$text = "Hello World";
$length = strlen($text); // 11

// For multibyte strings
$text = "Héllo Wörld";
$length = mb_strlen($text, 'UTF-8'); // 11

Character Access

$text = "Hello";
$firstChar = $text[0]; // 'H'
$lastChar = $text[strlen($text) - 1]; // 'o'
$thirdChar = $text{2}; // 'l' (curly braces syntax, deprecated)

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String Manipulation Functions

Case Conversion

$text = "Hello World";

$upper = strtoupper($text); // "HELLO WORLD"
$lower = strtolower($text); // "hello world"
$title = ucwords($text); // "Hello World"
$sentence = ucfirst(strtolower($text)); // "Hello world"

Trimming

$text = "  Hello World  ";

$trimmed = trim($text); // "Hello World"
$leftTrimmed = ltrim($text); // "Hello World  "
$rightTrimmed = rtrim($text); // "  Hello World"

// Trim specific characters
$text = "...Hello World...";
$cleaned = trim($text, '.'); // "Hello World"

String Searching

$text = "The quick brown fox jumps over the lazy dog";

// Find position of substring
$pos = strpos($text, "fox"); // 16
$pos = stripos($text, "FOX"); // 16 (case-insensitive)

// Check if string contains substring
if (str_contains($text, "fox")) { // PHP 8+
    echo "Found fox!";
}

// Count occurrences
$count = substr_count($text, "the"); // 1
$count = substr_count(strtolower($text), "the"); // 2 (case-insensitive)

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String Formatting

sprintf Function

$name = "John";
$age = 25;
$formatted = sprintf("Hello, %s! You are %d years old.", $name, $age);
// "Hello, John! You are 25 years old."

// Number formatting
$price = 1234.567;
$formatted = sprintf("Price: $%.2f", $price); // "Price: $1234.57"

printf Function

$name = "Alice";
$score = 95.5;
printf("Student: %-10s Score: %6.2f%%\n", $name, $score);
// Output: "Student: Alice      Score:  95.50%"

Number Formatting

$number = 1234567.89;

$formatted = number_format($number); // "1,234,568"
$formatted = number_format($number, 2); // "1,234,567.89"
$formatted = number_format($number, 2, ",", "."); // "1.234.567,89"

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String Replacement

$text = "The quick brown fox";

// Replace all occurrences
$newText = str_replace("fox", "dog", $text); // "The quick brown dog"

// Case-insensitive replacement
$newText = str_ireplace("QUICK", "slow", $text); // "The slow brown fox"

// Replace multiple values
$search = ["quick", "brown"];
$replace = ["slow", "black"];
$newText = str_replace($search, $replace, $text); // "The slow black fox"

// Count replacements
$newText = str_replace("fox", "dog", $text, $count);
echo "Made $count replacements";

Substring Operations

$text = "Hello World";

// Extract substring
$sub = substr($text, 0, 5); // "Hello"
$sub = substr($text, 6); // "World"
$sub = substr($text, -5); // "World" (from end)
$sub = substr($text, -5, 3); // "Wor"

// Multibyte substring
$text = "Héllo Wörld";
$sub = mb_substr($text, 0, 5, 'UTF-8'); // "Héllo"

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String Splitting and Joining

Explode and Implode

// Split string into array
$csv = "apple,banana,orange";
$fruits = explode(",", $csv); // ["apple", "banana", "orange"]

// Join array into string
$joined = implode(" | ", $fruits); // "apple | banana | orange"

// Limit splits
$text = "one-two-three-four";
$parts = explode("-", $text, 2); // ["one", "two-three-four"]

String Tokenization

$text = "apple,banana;orange:grape";
$token = strtok($text, ",;:");

while ($token !== false) {
    echo $token . "\n";
    $token = strtok(",;:");
}
// Outputs: apple, banana, orange, grape

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String Encoding and Security

HTML Escaping

$userInput = '<script>alert("XSS")</script>';
$safe = htmlspecialchars($userInput, ENT_QUOTES, 'UTF-8');
// "&lt;script&gt;alert(&quot;XSS&quot;)&lt;/script&gt;"

$decoded = htmlspecialchars_decode($safe);
// Back to original string

URL Encoding

$url = "Hello World & More";
$encoded = urlencode($url); // "Hello+World+%26+More"
$rawEncoded = rawurlencode($url); // "Hello%20World%20%26%20More"

$decoded = urldecode($encoded); // Back to original

Base64 Encoding

$data = "Hello World";
$encoded = base64_encode($data); // "SGVsbG8gV29ybGQ="
$decoded = base64_decode($encoded); // "Hello World"

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Multibyte String Handling

UTF-8 Support

// Set internal encoding
mb_internal_encoding('UTF-8');

$text = "Héllo Wörld";
$length = mb_strlen($text); // Correct length for multibyte
$upper = mb_strtoupper($text); // "HÉLLO WÖRLD"
$sub = mb_substr($text, 0, 5); // "Héllo"

Character Encoding Conversion

$text = "Hello World";
$converted = mb_convert_encoding($text, 'UTF-8', 'ISO-8859-1');

// Detect encoding
$encoding = mb_detect_encoding($text, ['UTF-8', 'ISO-8859-1']);

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String Comparison

Basic Comparison

$str1 = "apple";
$str2 = "Apple";

// Case-sensitive comparison
$result = strcmp($str1, $str2); // > 0 (str1 > str2)

// Case-insensitive comparison
$result = strcasecmp($str1, $str2); // 0 (equal)

// Natural order comparison
$files = ["file1.txt", "file10.txt", "file2.txt"];
usort($files, 'strnatcmp');
// Result: ["file1.txt", "file2.txt", "file10.txt"]

String Similarity

$str1 = "programming";
$str2 = "programing";

similar_text($str1, $str2, $percent);
echo "Similarity: " . round($percent, 2) . "%";

// Levenshtein distance
$distance = levenshtein($str1, $str2); // Number of edits needed

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Advanced String Operations

String Hashing

$password = "mySecretPassword";

// Simple hash (not secure for passwords)
$md5 = md5($password);
$sha1 = sha1($password);

// Secure password hashing
$hash = password_hash($password, PASSWORD_DEFAULT);
$isValid = password_verify($password, $hash);

String Parsing

// Parse URL
$url = "https://example.com/path?param=value";
$parsed = parse_url($url);
/*
Array(
    [scheme] => https
    [host] => example.com
    [path] => /path
    [query] => param=value
)
*/

// Parse query string
$query = "name=John&age=25&city=New+York";
parse_str($query, $params);
// $params = ["name" => "John", "age" => "25", "city" => "New York"]

String Templating

class StringTemplate {
    public static function render($template, $vars) {
        return preg_replace_callback('/\{\{(\w+)\}\}/', function($matches) use ($vars) {
            return isset($vars[$matches[1]]) ? $vars[$matches[1]] : $matches[0];
        }, $template);
    }
}

$template = "Hello, {{name}}! You are {{age}} years old.";
$vars = ["name" => "John", "age" => 25];
$result = StringTemplate::render($template, $vars);
// "Hello, John! You are 25 years old."

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Common String Patterns

CSV Handling

// Reading CSV data
$csvLine = '"John Doe","25","Engineer","New York"';
$data = str_getcsv($csvLine);
// ["John Doe", "25", "Engineer", "New York"]

// Creating CSV data
$data = ["John Doe", "25", "Engineer", "New York"];
$csvLine = '"' . implode('","', $data) . '"';

Path Operations

$path = "/var/www/html/index.php";

$dirname = dirname($path); // "/var/www/html"
$basename = basename($path); // "index.php"
$filename = pathinfo($path, PATHINFO_FILENAME); // "index"
$extension = pathinfo($path, PATHINFO_EXTENSION); // "php"

// Build path
$newPath = $dirname . DIRECTORY_SEPARATOR . "config.php";

JSON String Handling

$data = ["name" => "John", "age" => 25];
$json = json_encode($data); // '{"name":"John","age":25}'

$decoded = json_decode($json, true); // Back to array
$object = json_decode($json); // As stdClass object

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Performance Considerations

String Concatenation Performance

// Inefficient for many concatenations
$result = "";
for ($i = 0; $i < 1000; $i++) {
    $result .= "item $i ";
}

// More efficient approach
$items = [];
for ($i = 0; $i < 1000; $i++) {
    $items[] = "item $i";
}
$result = implode(" ", $items);