Network Card Device Driver Programming

Dear Developers

I am a network engineering student using LINUX for the first time. I have been assigned the project of tapping outgoing data from the network card of a computer running LINUX. I basically have to find the relevant device driver file and then somehow make it output to a file.  
The second part is to make a GUI to view the outgoing data from the computer in readable format.

I have located the relevant device driver file in the system. It is a c file called natsemi.c. I want to make the driver output the outgoing data to a file or to the screen so that I can pipe it to a file. For this I need to modify the device driver code which I am having trouble with. I have written a code is C which uses fopen,fgetc,fclose functions and should output the data to a new file. It is however not compiling because of problems with header files like stdio.h and stdlib.h. Could you please, please help me...

I am using Red Hat LINUX 8 and my network card is Netgear 311 ethernet adapter.

Thanks a lot for your help.

Regards
Navinder Kaplish
Ph: ++44 (0) 7939 840544