GetHostName.c

// GetHostName.c
//
// Prints current host's name in localized, human-readable format to stdout
//
// Compile using:
// cc -framework SystemConfiguration -framework CoreFoundation -o GetHostName GetHostName.c
//

#include <SystemConfiguration/SystemConfiguration.h>

#define f_strdup strdup

char * GetHostName()
{
    SCPreferencesRef prefs = SCPreferencesCreate(NULL, CFSTR("GetHostName"), NULL);         // Get system preferences handle, arg2=calling process name

    Boolean success = SCPreferencesLock(prefs, TRUE);                                       // arg2: TRUE = wait for lock

    // TODO: check lock or proceed without locking

    CFDictionaryRef systemPreferences = SCPreferencesGetValue(prefs, CFSTR("System"));      // Get "System" properties
    CFDictionaryRef systemDict = CFDictionaryGetValue(systemPreferences, CFSTR("System"));  // Get "System" dictionary (from "System" properties... I know.)
    CFStringRef hostName = CFDictionaryGetValue(systemDict, CFSTR("ComputerName"));

    success = SCPreferencesUnlock(prefs);

    const char * hostNameCString = CFStringGetCStringPtr(hostName, kCFStringEncodingUTF8);  // Convert to UTF-8 const char *
    
    // This function [CFStringGetCStringPtr] either returns the requested pointer immediately
    // with no memory allocations and no copying, in constant time, or returns NULL.
    //
    // TODO: if CFStringGetCStringPtr returns NULL, use slower CFStringGetCString
    
    CFRelease(prefs);                                                                       // Release system preferences handle

    return f_strdup(hostNameCString);
}

int main(int argc, char** argv)
{
    char * hostName = GetHostName();

    printf("%s\n", hostName);

    return 0;
}