https://security.web.cern.ch/security/recommendations/en/codetools/c.shtml

fgets.c

#include <stdio.h>
#include <stdlib.h>
#define LENGTH 8
int main () {
    char* username, *nlptr;
    int allow = 0;
 
    username = malloc(LENGTH * sizeof(*username));
    if (!username)
        return EXIT_FAILURE;
    printf external link("Enter your username, please: ");
    fgets(username,LENGTH, stdin);
    // fgets stops after LENGTH-1 characters or at a newline character, which ever comes first.
    // but it considers \n a valid character, so you might want to remove it:
    nlptr = strchr(username, '\n');
    if (nlptr) *nlptr = '\0';
 
    if (grantAccess(username)) {
        allow = 1;
    }
    if (allow != 0) {
        priviledgedAction();
    }
 
    free(username);
 
    return 0;
}