Platform-Independent Guid Generation in C++

Platform-independent GUID generation in C++?

If you can afford to use Boost, then there is a UUID library that should do the trick. It's very straightforward to use - check the documentation and this answer.

How to generate a GUID in C?

You can either use or look at the code of Boost.Uuid :

http://www.boost.org/doc/libs/1_47_0/libs/uuid/index.html

It is a C++ library, but still, you can find inside how the code author retrieved the Uuid on multiple systems. Last time I checked (january 2010), I found at least the following implementations for Windows and Linux/Solaris (this info could be outdated):

UUID/GUID on Linux/Solaris

Open a file to /dev/urandom and read enough bytes (16) to make up a GUID/UUID.

UUID/GUID on Windows

Use the following WinAPI functions

• CryptAcquireContext to acquire a random context
• CryptReleaseContext to release the acquired random context
• CryptGenRandom to generate enough bytes to make up a GUID/UUID

Other implementations

The Wikipedia page on GUID/UUID has a list of alternative implementations you could use/study:

https://en.wikipedia.org/wiki/UUID#Implementations

About your conditions

There is a GUID/UUID type which is always random (the version 4), meaning that to be compatible with other GUID/UUID semantics, you should respect that.

Now, you want the GUID/UUID to be ordered in time. The only way to do that without weakening the GUID/UUID randomness would be to prefix the 16-byte GUID/UUID with an unsigned integer (which would make your identifier data 20-bytes, or more, depending on your integer). Just generate a GUID/UUID, and increase the integer.

Simple Generation of GUID in C

CoCreateGuid is standard for all forms of Windows. Linux standard is libuuid, which is standard on all Linux versions and should be lightweight. I don't know of any library that will work for both Windows and Unix. I think that an #if branch for Windows and Linux is actually appropriate here.

Example of UUID generation using Boost in C++

A basic example:

#include <boost/uuid/uuid.hpp>            // uuid class
#include <boost/uuid/uuid_generators.hpp> // generators
#include <boost/uuid/uuid_io.hpp>         // streaming operators etc.

int main() {
    boost::uuids::uuid uuid = boost::uuids::random_generator()();
    std::cout << uuid << std::endl;
}

Example output:

7feb24af-fc38-44de-bc38-04defc3804de

How to obtain (almost) unique system identifier in a cross platform way?

To generate a mostly unique machine id, you can get a few serial numbers from various pieces of hardware on the system. Most processors will have a CPU serial number, the hard disks each have a number, and each network card will have a unique MAC address.

You can get these and build a fingerprint for the machine. You might want to allow some of these numbers to change before declaring it a new machine. ( e.g. if the 2 out of three are the same, then the machine is the same ). So you can deal somewhat gracefully from having a component upgraded.

I've clipped some code from one of my projects that gets these numbers.

Windows:

#include "machine_id.h"   

#define WIN32_LEAN_AND_MEAN        
#include <windows.h>      
#include <intrin.h>       
#include <iphlpapi.h>     
#ifndef _MSC_VER
#include <cpuid.h>
#else
#include <intrin.h>
#endif

// we just need this for purposes of unique machine id. So any one or two mac's is       
// fine. 
u16 hashMacAddress( PIP_ADAPTER_INFO info )          
{        
   u16 hash = 0;          
   for ( u32 i = 0; i < info->AddressLength; i++ )   
   {     
      hash += ( info->Address[i] << (( i & 1 ) * 8 ));        
   }     
   return hash;           
}        

void getMacHash( u16& mac1, u16& mac2 )              
{        
   IP_ADAPTER_INFO AdapterInfo[32];                  
   DWORD dwBufLen = sizeof( AdapterInfo );           

   DWORD dwStatus = GetAdaptersInfo( AdapterInfo, &dwBufLen );                  
   if ( dwStatus != ERROR_SUCCESS )                  
      return; // no adapters.      

   PIP_ADAPTER_INFO pAdapterInfo = AdapterInfo;      
   mac1 = hashMacAddress( pAdapterInfo );            
   if ( pAdapterInfo->Next )       
      mac2 = hashMacAddress( pAdapterInfo->Next );   

   // sort the mac addresses. We don't want to invalidate     
   // both macs if they just change order.           
   if ( mac1 > mac2 )     
   {     
      u16 tmp = mac2;     
      mac2 = mac1;        
      mac1 = tmp;         
   }     
}        

u16 getVolumeHash()       
{        
   DWORD serialNum = 0;   

   // Determine if this volume uses an NTFS file system.      
   GetVolumeInformation( "c:\\", NULL, 0, &serialNum, NULL, NULL, NULL, 0 );    
   u16 hash = (u16)(( serialNum + ( serialNum >> 16 )) & 0xFFFF );              

   return hash;           
}        

u16 getCpuHash()          
{        
   int cpuinfo[4] = { 0, 0, 0, 0 };                  
   __cpuid( cpuinfo, 0 );          
   u16 hash = 0;          
   u16* ptr = (u16*)(&cpuinfo[0]); 
   for ( u32 i = 0; i < 8; i++ )   
      hash += ptr[i];     

   return hash;           
}        

const char* getMachineName()       
{        
   static char computerName[1024]; 
   DWORD size = 1024;     
   GetComputerName( computerName, &size );           
   return &(computerName[0]);      
}

Linux and OsX:

#include <stdio.h>
#include <string.h>
#include <unistd.h>          
#include <errno.h>           
#include <sys/types.h>       
#include <sys/socket.h>      
#include <sys/ioctl.h>  
#include <sys/resource.h>    
#include <sys/utsname.h>       
#include <netdb.h>           
#include <netinet/in.h>      
#include <netinet/in_systm.h>                 
#include <netinet/ip.h>      
#include <netinet/ip_icmp.h> 
#include <assert.h>

#ifdef DARWIN                    
#include <net/if_dl.h>       
#include <ifaddrs.h>         
#include <net/if_types.h>    
#else //!DARWIN              
// #include <linux/if.h>        
// #include <linux/sockios.h>   
#endif //!DARWIN               

const char* getMachineName() 
{ 
   static struct utsname u;  

   if ( uname( &u ) < 0 )    
   {       
      assert(0);             
      return "unknown";      
   }       

   return u.nodename;        
}   

//---------------------------------get MAC addresses ------------------------------------unsigned short-unsigned short----------        
// we just need this for purposes of unique machine id. So any one or two mac's is fine.            
unsigned short hashMacAddress( unsigned char* mac )                 
{ 
   unsigned short hash = 0;             

   for ( unsigned int i = 0; i < 6; i++ )              
   {       
      hash += ( mac[i] << (( i & 1 ) * 8 ));           
   }       
   return hash;              
} 

void getMacHash( unsigned short& mac1, unsigned short& mac2 )       
{ 
   mac1 = 0;                 
   mac2 = 0;                 

#ifdef DARWIN                

   struct ifaddrs* ifaphead; 
   if ( getifaddrs( &ifaphead ) != 0 )        
      return;                

   // iterate over the net interfaces         
   bool foundMac1 = false;   
   struct ifaddrs* ifap;     
   for ( ifap = ifaphead; ifap; ifap = ifap->ifa_next )                  
   {       
      struct sockaddr_dl* sdl = (struct sockaddr_dl*)ifap->ifa_addr;     
      if ( sdl && ( sdl->sdl_family == AF_LINK ) && ( sdl->sdl_type == IFT_ETHER ))                 
      {    
          if ( !foundMac1 )  
          {                  
             foundMac1 = true;                
             mac1 = hashMacAddress( (unsigned char*)(LLADDR(sdl))); //sdl->sdl_data) + sdl->sdl_nlen) );       
          } else {           
             mac2 = hashMacAddress( (unsigned char*)(LLADDR(sdl))); //sdl->sdl_data) + sdl->sdl_nlen) );       
             break;          
          }                  
      }    
   }       

   freeifaddrs( ifaphead );  

#else // !DARWIN             

   int sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_IP );                  
   if ( sock < 0 ) return;   

   // enumerate all IP addresses of the system         
   struct ifconf conf;       
   char ifconfbuf[ 128 * sizeof(struct ifreq)  ];      
   memset( ifconfbuf, 0, sizeof( ifconfbuf ));         
   conf.ifc_buf = ifconfbuf; 
   conf.ifc_len = sizeof( ifconfbuf );        
   if ( ioctl( sock, SIOCGIFCONF, &conf ))    
   {       
      assert(0);             
      return;                
   }       

   // get MAC address        
   bool foundMac1 = false;   
   struct ifreq* ifr;        
   for ( ifr = conf.ifc_req; (char*)ifr < (char*)conf.ifc_req + conf.ifc_len; ifr++ ) 
   {       
      if ( ifr->ifr_addr.sa_data == (ifr+1)->ifr_addr.sa_data )          
         continue;  // duplicate, skip it     

      if ( ioctl( sock, SIOCGIFFLAGS, ifr ))           
         continue;  // failed to get flags, skip it    
      if ( ioctl( sock, SIOCGIFHWADDR, ifr ) == 0 )    
      {    
         if ( !foundMac1 )   
         { 
            foundMac1 = true;                 
            mac1 = hashMacAddress( (unsigned char*)&(ifr->ifr_addr.sa_data));       
         } else {            
            mac2 = hashMacAddress( (unsigned char*)&(ifr->ifr_addr.sa_data));       
            break;           
         } 
      }    
   }       

   close( sock );            

#endif // !DARWIN            

   // sort the mac addresses. We don't want to invalidate                
   // both macs if they just change order.    
   if ( mac1 > mac2 )        
   {       
      unsigned short tmp = mac2;        
      mac2 = mac1;           
      mac1 = tmp;            
   }       
} 

unsigned short getVolumeHash()          
{ 
   // we don't have a 'volume serial number' like on windows. Lets hash the system name instead.    
   unsigned char* sysname = (unsigned char*)getMachineName();       
   unsigned short hash = 0;             

   for ( unsigned int i = 0; sysname[i]; i++ )         
      hash += ( sysname[i] << (( i & 1 ) * 8 ));       

   return hash;              
} 

#ifdef DARWIN                
 #include <mach-o/arch.h>    
 unsigned short getCpuHash()            
 {         
     const NXArchInfo* info = NXGetLocalArchInfo();    
     unsigned short val = 0;            
     val += (unsigned short)info->cputype;               
     val += (unsigned short)info->cpusubtype;            
     return val;             
 }         

#else // !DARWIN             

 static void getCpuid( unsigned int* p, unsigned int ax )       
 {         
    __asm __volatile         
    (   "movl %%ebx, %%esi\n\t"               
        "cpuid\n\t"          
        "xchgl %%ebx, %%esi" 
        : "=a" (p[0]), "=S" (p[1]),           
          "=c" (p[2]), "=d" (p[3])            
        : "0" (ax)           
    );     
 }         

 unsigned short getCpuHash()            
 {         
    unsigned int cpuinfo[4] = { 0, 0, 0, 0 };          
    getCpuid( cpuinfo, 0 );  
    unsigned short hash = 0;            
    unsigned int* ptr = (&cpuinfo[0]);                 
    for ( unsigned int i = 0; i < 4; i++ )             
       hash += (ptr[i] & 0xFFFF) + ( ptr[i] >> 16 );   

    return hash;             
 }         
#endif // !DARWIN            

int main()
{

  printf("Machine: %s\n", getMachineName());
  printf("CPU: %d\n", getCpuHash());
  printf("Volume: %d\n", getVolumeHash());
  return 0;
}    

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