Negative return value in open system call for file created in /proc file system

Question

I have created a file in /proc named "test" (it was created in kernel). The file exists. When I want to open it in user level it returns negative.

int fd;
if((fd=open("/proc/test","O_RDONLY"))<0){ 
      perror("open"); 
}

The error that I see is open: File exists. I have seen this question but it is not my case.

Answer 1

You need parentheses in there (now fixed in the question), and the second argument to open() is not a string:

#include <fcntl.h>

int fd;
if ((fd = open("/proc/test", O_RDONLY)) < 0)
    perror("open");

I'm not convinced it was a good idea to create a file of any sort in the /proc file system. In fact, I'm a bit surprised you were allowed to. If you are learning to program as root, I hope you have good backups.