PHP $_POST Undefined index but var_dump works

Question

when I do

var_dump($_POST); 

I have the following result :

'apk' => string 'apk_techs.apk' (length=13)

which is what I'm expecting, but when I do

readFile("./".$_POST['apk']);

it throws the following error

[09-Jun-2017 10:14:00 UTC] PHP Warning:  readfile(./): failed to open stream: No such file or directory in C:\wamp64\www\atawa_api\api_techs.php on line 848

Can someone tell me about somthing I would ignore ?

EDIT

The path is correct and it is only for debugging, the problem isn't that path is incorrect or not found, but not given (considering the undefined index).

Answer 1

for readfile function you have to pass the complete path of file. eg like below : readFile("/var/www/tttt.apk");