Get Computer Name and logged user name

Question

I am developing an application. One of the methods needs to capture the computer name and user logged on the machine, then display both to the user. I need it to run on both Windows and Linux. What is the best way to do this?

Answer 1

Windows

You can try to use GetComputerName and GetUserName, here is a example:

#define INFO_BUFFER_SIZE 32767
TCHAR  infoBuf[INFO_BUFFER_SIZE];
DWORD  bufCharCount = INFO_BUFFER_SIZE;

// Get and display the name of the computer.
if( !GetComputerName( infoBuf, &bufCharCount ) )
  printError( TEXT("GetComputerName") ); 
_tprintf( TEXT("\nComputer name:      %s"), infoBuf ); 

// Get and display the user name.
if( !GetUserName( infoBuf, &bufCharCount ) )
  printError( TEXT("GetUserName") ); 
_tprintf( TEXT("\nUser name:          %s"), infoBuf );

see: GetComputerName and GetUserName

Linux

Use gethostname to get computer name(see gethostname), and getlogin_r to get login username. You can look more information at man page of getlogin_r. Simple usage as follows:

#include <unistd.h>
#include <limits.h>

char hostname[HOST_NAME_MAX];
char username[LOGIN_NAME_MAX];
gethostname(hostname, HOST_NAME_MAX);
getlogin_r(username, LOGIN_NAME_MAX);

Answer 2

If you can use Boost, you can do this to easily get the host name:

#include <boost/asio/ip/host_name.hpp>
// ... whatever ...
const auto host_name = boost::asio::ip::host_name();

Answer 3

On POSIX systems you can use the gethostname and getlogin functions, both declared in unistd.h.

/*
   This is a C program (I've seen the C++ tag too late).  Converting
   it to a pretty C++ program is left as an exercise to the reader.
*/

#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int
main()
{
  char hostname[HOST_NAME_MAX];
  char username[LOGIN_NAME_MAX];
  int result;
  result = gethostname(hostname, HOST_NAME_MAX);
  if (result)
    {
      perror("gethostname");
      return EXIT_FAILURE;
    }
  result = getlogin_r(username, LOGIN_NAME_MAX);
  if (result)
    {
      perror("getlogin_r");
      return EXIT_FAILURE;
    }
  result = printf("Hello %s, you are logged in to %s.\n",
                  username, hostname);
  if (result < 0)
    {
      perror("printf");
      return EXIT_FAILURE;
    }
  return EXIT_SUCCESS;
}

Possible output:

Hello 5gon12eder, you are logged in to example.com.

This seems safer than relying on environment variables which are not always present.

I'm withdrawing that last statement because

• the man page of getlogin actually discourages its usage in favour of getenv("LOGIN") and
• the getlogin_r call in the above program fails with ENOTTY when I run the program from within Emacs instead of an interactive terminal while getenv("USER") would have worked in both situations.

Answer 4

Use gethostname() to get computer name, support both windows and linux.

Answer 5

Regarding Denis's answer, note that getenv("HOSTNAME") for Linux may not always work because the environment variables may not be exported to the program.

Multi-platform C++ code example to fetch just the computer name (this is what worked for my Win7 and CentOS machines):

    char *temp = 0;
    std::string computerName;

#if defined(WIN32) || defined(_WIN32) || defined(_WIN64)
    temp = getenv("COMPUTERNAME");
    if (temp != 0) {
        computerName = temp;
        temp = 0;
    }
#else
    temp = getenv("HOSTNAME");
    if (temp != 0) {
        computerName = temp;
        temp = 0;
    } else {
        temp = new char[512];
        if (gethostname(temp, 512) == 0) { // success = 0, failure = -1
            computerName = temp;
        }
        delete []temp;
        temp = 0;
    }
#endif

Answer 6

in Linux you can also use the following using Posix library to retrieve the real user that owns the process: getuid() returns the real user ID of the calling process. see getuid man page

#include <pwd.h>
string userName = "unknownUser";
// Structure to store user info
struct passwd p;
// Get user ID of the application
uid_t uid = getuid();

// Buffer that contains password additional information
char pwdBuffer[ourPwdBufferSize];
// Temporary structure for reentrant function
struct passwd* tempPwdPtr;

if ((getpwuid_r(uid, &p, pwdBuffer, sizeof(pwdBuffer),
        &tempPwdPtr)) == 0) {
    userName = p.pw_name;
}