使用此功能可以安全地防止“SQL注入”吗？

Question

Many days ago, my friend read this question: How can I prevent SQL injection in PHP?. And, I know that there are many good answers to solve this problem.

I have a friend, who is working with PHP better than me. Yesterday, he said to me: "There are many good answers, in here. But, can you write other code for solving this problem?".

He still uses PHP 4; so, he do not like to use any mysqli_ function, not me.

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So, I have created a simple function, in PHP:

<?php

function MyFun($MyVar)

{
    if(!get_magic_quotes_gpc()) { $MyVar = addslashes($MyVar); }

    $MyVar = strip_tags($MyVar);
    $MyVar = htmlentities($MyVar);

    return trim($MyVar);

}

?>

I used my function in every $_POST[]; or $_GET[];, for instance:

$Var1 = MyFun($_POST['Txt1']);
$Var2 = MyFun($_GET['Txt2']);

My friend said that: "It can not prevent any SQL injection.". I do not think so.

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Can you tell me: "Is it safe to prevent SQL injection, with this function?".