Error Handling and Runtime Exceptions

Try/Catch

Use try/catch to handle errors gracefully instead of crashing:

try {
    // Code that might fail
    $result = riskyOperation();
} catch (Exception $e) {
    // Handle the error
    echo "Error: " . $e->getMessage();
}

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Throwing Exceptions

Use throw to signal an error:

function divide($a, $b) {
    if ($b === 0) {
        throw new Exception("Cannot divide by zero");
    }
    return $a / $b;
}

try {
    echo divide(10, 0);
} catch (Exception $e) {
    echo $e->getMessage();  // "Cannot divide by zero"
}

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Exception Methods

Exceptions provide useful information about what went wrong:

try {
    throw new Exception("Something failed", 500);
} catch (Exception $e) {
    echo $e->getMessage();  // "Something failed"
    echo $e->getCode();     // 500
    echo $e->getFile();     // File where exception was thrown
    echo $e->getLine();     // Line number
}

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Multiple Catch Blocks

Handle different exception types separately:

try {
    // Code that might throw different exceptions
    $data = fetchData();
} catch (InvalidArgumentException $e) {
    echo "Invalid input: " . $e->getMessage();
} catch (RuntimeException $e) {
    echo "Runtime error: " . $e->getMessage();
} catch (Exception $e) {
    echo "General error: " . $e->getMessage();
}

Order matters - catch specific exceptions first, then general ones.

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Common Exception Types

Exception	Use Case
Exception	General errors
InvalidArgumentException	Invalid function arguments
RuntimeException	Errors during execution
PDOException	Database errors
TypeError	Wrong type passed to function

function setAge(int $age) {
    if ($age < 0) {
        throw new InvalidArgumentException("Age cannot be negative");
    }
}

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Finally Block

Code in finally always runs, whether an exception occurred or not:

try {
    $file = fopen("data.txt", "r");
    // Process file
} catch (Exception $e) {
    echo "Error: " . $e->getMessage();
} finally {
    fclose($file);  // Always close the file
}

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Example

function getUser($id) {
    if ($id <= 0) {
        throw new Exception("Invalid user ID");
    }

    // Simulate database lookup
    $users = [1 => "John", 2 => "Jane"];

    if (!isset($users[$id])) {
        throw new Exception("User not found");
    }

    return $users[$id];
}

try {
    $user = getUser(5);
    echo "Hello, $user";
} catch (Exception $e) {
    echo "Error: " . $e->getMessage();  // "User not found"
}