Use str_split to verify whether user input is legal

In PHP, str_split() is a very useful function that can split strings into character arrays. This function is especially useful when we need to process the content input by the user at a character level. For example, if we want to check whether user input is legal, we can combine str_split() to achieve this function.

Below we will explain in detail how to use str_split() to split user input and verify whether each character is legal.

Step 1: Obtain user input

Usually, we get user input through HTML forms. We can use $_POST or $_GET to get form data. For simplicity, suppose we have a simple HTML form containing user input:

 <form method="post" action="validate.php">
    <input type="text" name="user_input" placeholder="Please enter content" />
    <button type="submit">submit</button>
</form>

In validate.php , we will process user input.

Step 2: Use str_split() to split the user input character by character

We can split the string input by the user into a character array through the str_split() function. This way, we can process it character by character.

 <?php
if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $user_input = $_POST['user_input'];

    // use str_split Split the input into a character array
    $chars = str_split($user_input);
    
    // Print split character array
    print_r($chars);
}
?>

The above code will split the string entered by the user into an array of characters and output it. For example, the input string hello will become ['h', 'e', ​​'l', 'l', 'o'] .

Step 3: Verify whether each character is legal

Suppose we need to check whether each character is a letter (i.e. whether it meets the letter requirements). We can use the ctype_alpha() function to verify whether the character is a letter.

 <?php
if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $user_input = $_POST['user_input'];

    // use str_split Split the input into a character array
    $chars = str_split($user_input);

    // Verify that each character is legal
    foreach ($chars as $char) {
        if (!ctype_alpha($char)) {
            echo "Illegal characters：$char<br>";
        }
    }
}
?>

In this example, we loop through each character and use ctype_alpha() to check if it is a letter. If a character is not a letter, the system will prompt an illegal character.

Step 4: Process and output results

To make the result more user-friendly, we can collect all illegal characters and give prompt information.

 <?php
if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $user_input = $_POST['user_input'];

    // use str_split Split the input into a character array
    $chars = str_split($user_input);
    $invalid_chars = [];

    // Verify that each character is legal
    foreach ($chars as $char) {
        if (!ctype_alpha($char)) {
            $invalid_chars[] = $char;
        }
    }

    // 如果有Illegal characters，Output
    if (count($invalid_chars) > 0) {
        echo "The following characters are illegal： " . implode(', ', $invalid_chars);
    } else {
        echo "All characters entered are valid！";
    }
}
?>

In this example, all illegal characters are collected into the $invalid_chars array and concatenated into a string through the implode() function, and finally output.

Step 5: Verify using URL

If you need to access certain resources through URLs during the verification process, you can use curl or file_get_contents to verify certain external resources. Assuming you need to verify the data of an external API, we can do this: