Check if PHP session has already started

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I have a PHP file that is sometimes
called from a page that has started a session and sometimes from a page that doesn't
have session started. Therefore when I have session_start() on
this script I sometimes get the error message for "session already started". For that
I've put these
lines:

if(!isset($_COOKIE["PHPSESSID"]))
{

            session_start();
}

but
this time I got this warning
message:

Notice:
Undefined variable: _SESSION

Is
there a better way to check if session has already
started?

If I use
@session_start will it make things work properly and just shut
up the warnings?

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class="normal">Answer

Recommended way for versions of
PHP >= 5.4.0 , PHP
7

if
            (session_status() == PHP_SESSION_NONE) {

            session_start();

}

Reference:
rel="noreferrer">http://www.php.net/manual/en/function.session-status.php

For
versions of PHP <
5.4.0

if(session_id()
            == '') {

            session_start();
}