Check if user is root in C?

Question

How can I verify if the user is root?

Answer 1

getuid or geteuid, depending on what you really mean. In either case, 0 means root.

if(geteuid() != 0)
{
  // Tell user to run app as root, then exit.
}

The point made by R is valid. You should consider trial and error, or another approach that does not explicitly require root.