Php cannot write to file in android [on hold]

Php cannot write to file in android [on hold]

I have developed a webserver which support php,mysql it runs fine but the
when i run a php script that writes text to a text file it can not write
to the file but the file size is diferrent but i cannot see the text.Do i
have to make a permission in it or any thing wrong with the conf file
Please help me..
I use fopen to open the text file and apped it:
fopen("log.txt","a");