PHP contact form, am I doing it wrong?

I'm learning PHP and I'm trying to write a simple email script. I have a function (checkEmpty) to check if all the forms are filled in and if the email adress is valid (isEmailValid). I'm not sure how to return true checkEmpty funciton. Here's my code:

When the submit button is clicked:

if (isset($_POST['submit'])) {

//INSERT FORM VALUES INTO AN ARRAY
$field = array ('name' => $_POST['name'], 'email' => $_POST['email'], 'message' => $_POST['message']);

//CONVERT ARRAY KEYS TO VARIABLE NAMES
extract ($field);
checkEmpty($name, $email, $message);



function checkEmpty($name, $email, $message) {  
    global $name_error;
    global $mail_error;
    global $message_error;

    //CHECK IF NAME FIELD 开发者_如何学CIS EMPTY
    if (isset($name) === true && empty($name) === true) {
    $name_error = "<span class='error_text'>* Please enter your name</span>";
    }

//CHECK IF EMAIL IS EMPTY
if (isset($email) === true && empty($email) === true) {
    $mail_error = "<span class='error_text'>* Please enter your email address</span>";
    //AND IF IT ISN'T EMPTY CHECK IF IT IS A VALID ONE
    } 
    elseif (!isValidEmail($email)) {
        $mail_error = "<span class='error_text'> * Please enter a valid email</span>"; 
    }

    //CHECK IF MESSAGE IS EMPTY
    if (isset($message) === true && empty($message) === true) {
    $message_error = "<span class='error_text'>* Please enter your message</span>";
    }
} 

// This function tests whether the email address is valid  
function isValidEmail($email){
    $pattern = "^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,3})$";
    if (eregi($pattern, $email))
        {
            return true;
        } else 
        {
            return false;
        }   
    }

I know I shouldn't be using globals in the function, I don't know an alternative. The error messages are display beside each form element.

First of all, using global is a sin. You are polluting global namespace, and this is bad idea, except little ad-hoc scripts and legacy code.

Second, you are misusing isset - for two reasons: a ) in given context you pass variable $name to function, so it is always set b ) empty checks whether variable is set or not

Third, you should separate validation from generating html.

Fourth, you can use filter_var instead of regular expression to test if mail is valid.

Last, your code could look like that:

<?php

if (isset($_POST['submit'])) {

$fields = array ('name' => $_POST['name'], 'email' => $_POST['email'], 'message' =>     $_POST['message']);

//CONVERT ARRAY KEYS TO VARIABLE NAMES
extract ($fields);  

$errors = validateFields($name, $email, $message);

if (!empty($errors)){

    # error 

    foreach ($errors as $error){

        print "<p class='error'>$error</p>";

    }

} else {

    # all ok, do your stuff

} // if

} // if

function validateFields($name, $email, $post){

    $errors = array();

        if (empty($name)){$errors[] = "Name can't be empty";}
        if (empty($email)){$errors[] = "Email can't be empty";}
        if (empty($post)){$errors[] = "Post can't be empty";}

        if (!empty($email) && !filter_var($email,FILTER_VALIDATE_EMAIL)){$errors[] = "Invalid email";}
        if (!empty($post) && strlen($post)<10){$errors[] = "Post too short (minimum 10 characters)";}

    # and so on...

    return $errors;

}

First of all, you should really re-think your logic as to avoid global variables.

Eitherway, create a variable $success and set it to true in the top of your functions. If any if statement fails, set it to false. Then return $success in the bottom of your function. Example:

function checkExample($txt) {
    $success = true;

    if (isset($txt) === true && empty($txt) === true) {
        $error = "<span class='error_text'>* Please enter your example text</span>";
        $success = false;
    }

    return $success;
}

I'm not sure this is what you want, the way I see it, you want $mail_error, $message_error and $name_error to be accessible from outside the function. If that's the case, what you need is something like this:

function checkEmpty($name, $email, $message) {  
    $results = false;

    //CHECK IF NAME FIELD IS EMPTY
    if (isset($name) === true && empty($name) === true) {
      $results['name_error'] = "<span class='error_text'>* Please enter your name</span>";
    }

    //CHECK IF EMAIL IS EMPTY
    if (isset($email) === true && empty($email) === true) {
      $results['mail_error'] = "<span class='error_text'>* Please enter your email address</span>";
    //AND IF IT ISN'T EMPTY CHECK IF IT IS A VALID ONE
    } 
    elseif (!isValidEmail($email)) {
        $results['mail_error'] = "<span class='error_text'> * Please enter a valid email</span>"; 
    }

    //CHECK IF MESSAGE IS EMPTY
    if (isset($message) === true && empty($message) === true) {
      $results['message_error'] = "<span class='error_text'>* Please enter your message</span>";
    }

    return $results;
} 
$errors = checkEmpty($name, $email, $message);

now you can test for errors

if($errors){
    extract ($errors); // or simply extract variables from array to be used next to form inputs
} else {
    // there are no errors, do other thing if needed...
}