How do I clear the whole contents of a file in C?

Question

I have a file with some of user1\'s data. I want to use the same file for user2 by clearing the content of the file.

My idea is that when a new user comes, data of

Answer 1

There are two ways:

1. fd=open(filename,O_RDONLY | O_WRONLY | O_TRUNC);


2. [cat /dev/null > filename] for BASH. It can be directly used in c program using [system()] system call. 

   system("cat /dev/null > filename");