How to check if a Post Id exists?

Hi all and thank you in advance.

The problem: I do not know how to check if a Post Id exists.

I wrote some code inside “single.php” to show “related posts” based upon “custom values” (the id’s separated by “|”) in a “custom field”.

The id’s are not checked in the “Edit Post” page; it is only a string like this “12|44|67”, freely written by me. I parse the string to obtain the single components – for example “12” “44” “67”.

Before printing the list of related posts by a loop, I have to check if those id’s exist.

The code in the following:

$ids_related_arr=get_post_custom_values('ids_related'); // ids_related contains for examples 12|44|67
if(isset($ids_related_arr)){
	foreach($ids_related_arr as $key=>$value){
		$ids_arr=explode('|',$value);
		foreach($ids_arr as $key_id=>$value_id){
			if(/* the Post with Id=$value_id exists */){
				// write the link to the post
			};
		};
	};
};