C Programming. Printing current user

Question

In C programming how do you get the current user and the current working directory. I'm trying to print something like this:

  asmith@mycomputer:~/Desktop/testProgram:$
  (user) (computerName) (current directory)

I have the following code, but the username is showing as NULL. Any ideas what I'm doing wrong?

void prompt()
{
        printf("%s@shell:~%s$", getenv("LOGNAME"), getcwd(currentDirectory, 1024));                 
}

Answer 1

Aside from the fact that you should be using the environment variable USER instead of LOGNAME, you shouldn't be using environment variables for this in the first place. You can get the current user ID with getuid(2) and the current effective user ID with geteuid(2), and then use getpwuid(3) to get the user name from the user ID from the passwd file:

struct passwd *p = getpwuid(getuid());  // Check for NULL!
printf("User name: %s\n", p->pw_name);

To get the current computer name, use gethostname(2):

char hostname[HOST_NAME_MAX+1];
gethostname(hostname, sizeof(hostname));  // Check the return value!
printf("Host name: %s\n", hostname);