I have this problem, it says Fatal error: Cannot use $this as parameter in [duplicate]

function before ($this, $inthat)
{
    return substr($inthat, 0, strpos($inthat, $this));
}
function between($this, $that, $inthat)
{
    return before ($that, after($this, $inthat));
}
function after ($this, $inthat)
{
    if (!is_bool(strpos($inthat, $this)))
    return substr($inthat, strpos($inthat,$this)+strlen($this));
}

Fatal error: Cannot use $this as parameter in /home/u550540499/domains/matureguide.in/public_html/application/helpers/global_helper.php
on line **991

We are facing this when we upload my website in hostinger hosting. Can anyone help to resolve it?