#include <iostream>
#include <fcntl.h>    // for open
#include <stdio.h>    // for perror
#include <string.h>   // for strerror
#include <unistd.h>   // for getpid


using namespace std;

int main() {
    int fd;
    int errorSave;

    cout << endl;
    cout << "Just so you know, EACCES is " << EACCES << endl;
    cout << "Just so you know, EBADF is " << EBADF << endl;
    cout << endl;

    // the right way.
    cout << endl << "Executing " << endl;
    cout << "fd = open(\"/etc/passwd\", O_RDWR);" << endl;
    fd = open("/etc/passwd", O_RDWR);
    if (-1 == fd) {
       
       // save it, perror might change it if there is a problem.
       errorSave = errno;
       perror("\tUnable to open /etc/passwd");

       cout << "\terrno = " << errno << " errorSave = " << errorSave << endl;

       // don't mess with these two strings
       // if you need them, save them as they might change later.
       cout << "\tThe error string is " << strerror(errorSave) << endl;
       cout << "\tThe error name is " << strerrorname_np(errorSave) << endl;

       // the error has been handled, reset it.
       errno = 0;
    }

    cout << endl << endl;

    // careful, any system call could reset the errno variable.
    cout << "EXECUTING: fd = open(\"/etc/passwd\", O_RDWR);" << endl;
    fd = open("/etc/passwd", O_RDWR);
    if (-1 == fd) {
       errorSave = errno;

       cout << "\terrno = " << errno << " errorSave = " << errorSave << endl;
       // force another system error.
       close(999);
       cout << "\terrno = " << errno << " errorSave = " << errorSave << endl;
       perror("Error from opening /etc/passwd");

       errno = 0;
    }

    cout << endl << endl;

    cout << "EXECUTING: if (-1 == fd = open(\"/etc/passwd\", O_RDWR) ) {" 
         << endl;

    // you will see this, but my compiler flags complained so I added ()
    // if (-1 == fd = open("/etc/passwd", O_RDWR) ) {
    if (-1 == (fd = open("/etc/passwd", O_RDWR)) ) {
       errorSave = errno;
       perror("\tERROR: opening /etc/passwd failed");
    }


    return 0;

}