Thread: Changing file pointer position

Dear Friends

I need your kind help urgently.
I'm writing a piece of program under Ubuntu attempting to open an existing file to update (read/write).I need
to move file pointer to any position in the file based on some calculations and alter the content. But the problem is that when I open the file using (fopen and "a"-mode) it writes always at the end of file and I cannot move backward(fseek has no effect). If I open it in "w"-mode it would be truncated (actually destroyed). The action (forcing the file pointer to set at any location of file) is something I used to do under DOS perfectly. Could you please suggest any solution for the issue?

Have you considered using the "+r" mode?

Some documentation for the open modes of fopen.

Originally Posted by jimblumberg

Have you considered using the "+r" mode?

Some documentation for the open modes of fopen.

"r" combinations stand for "Read Only", don't they?

Originally Posted by Sanfter

"r" combinations stand for "Read Only", don't they?

Please study the manpage for fopen() thoroughly, as jimblumberg gave you above! That will give you all the information you need!

Originally Posted by jimblumberg

Have you considered using the "+r" mode?

Some documentation for the open modes of fopen.

Dear jimblumberg

Thank you so much for your advice. You solved my problem.