How to get the username in C/C++ in Linux?

Question

How can I get the actual \"username\" without using the environment (getenv, ...) in a program?

Answer 1

Use char *cuserid(char *s) found in stdio.h.

#include 

#define MAX_USERID_LENGTH 32

int main()
{
  char username[MAX_USERID_LENGTH];
  cuserid(username);
  printf("%s\n", username);
  return 0;
}

See for more details:

1. https://pubs.opengroup.org/onlinepubs/007908799/xsh/cuserid.html
2. https://serverfault.com/questions/294121/what-is-the-maximum-username-length-on-current-gnu-linux-systems