largest value of the 2nd parameter in fgets function

hello i've tried to read a line from a text file by fgets($fp,8192). it work fine. however, there is a line over 8192 char and i tried to increase the 2nd parameter (e.g. 8193, 16384, 88192) still only 8192 char are read to my string variables. is it a limit of fgets or length of a string? any way to achieve getting more than 8192 char from a line in a text file? pls advice. terence