How to Find System Hostname in C

1. Use the gethostname Function to Find System Hostname in C
2. Use the uname Function to Find System Hostname in C

This article will explain several methods of how to find system hostname in C.

Use the gethostname Function to Find System Hostname in C

The gethostname function is part of the POSIX specification, and it’s used to access the system hostname. The function takes two arguments: char* pointing to a buffer where retrieved hostname will be stored and the number of bytes denoting the buffer’s length. The function returns zero on success, and -1 is returned on error. Note that POSIX systems are likely to have a maximum number of bytes defined for hostname length, so the user should allocate the big enough buffer to store the retrieved value.

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

enum { MAX_SIZE = 256 };

int main(void) {
  int ret;
  char hostname[MAX_SIZE];

  ret = gethostname(&hostname[0], MAX_SIZE);
  if (ret == -1) {
    perror("gethostname");
    exit(EXIT_FAILURE);
  }
  printf("Hostname:    %s\n", hostname);

  exit(EXIT_SUCCESS);
}

Output:

Hostname:    lenovo-pc

The previous example demonstrates the basic call to the gethostname function, but one should always implement error reporting routines to ensure fail-safe code and informative logging messages. Since the gethostname sets errno values, we can evaluate it in a switch statement and print the corresponding messages to the stderr stream.

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

enum { MAX_SIZE = 256 };

int main(void) {
  int ret;
  char hostname[MAX_SIZE];

  errno = 0;
  ret = gethostname(&hostname[0], MAX_SIZE);
  if (ret == -1) {
    switch (errno) {
      case EFAULT:
        fprintf(stderr, "'name' argument is an invalid address");
        break;
      case EINVAL:
        fprintf(stderr, "'len' argument is negative");
        break;
      default:
        perror("gethostname");
    }
    exit(EXIT_FAILURE);
  }
  printf("Hostname:    %s\n", hostname);

  exit(EXIT_SUCCESS);
}

Output:

Hostname:    lenovo-pc

Use the uname Function to Find System Hostname in C

Alternatively, one can utilize the uname function call to find the system hostname. uname can generally retrieve several data points about the system, namely the operating system name, operating system release date, and version, Hardware identifier, and hostname. Notice though, uname stores the above information in a utsntheame structure defined in <sys/utsname.h> header file. The function takes the pointer to the utsname structure and returns the zero value on a successful call. uname also sets errno on failure, and EFAULT value is defined as an indication when the passed pointer to a utsname structure is invalid.

#include <stdio.h>
#include <stdlib.h>
#include <sys/utsname.h>

enum { MAX_SIZE = 256 };

int main(void) {
  struct utsname uts;

  if (uname(&uts) == -1) perror("uname");

  printf("Node name:   %s\n", uts.nodename);
  printf("System name: %s\n", uts.sysname);
  printf("Release:     %s\n", uts.release);
  printf("Version:     %s\n", uts.version);
  printf("Machine:     %s\n", uts.machine);

  exit(EXIT_SUCCESS);
}

Output:

Hostname:    lenovo-pc