Getting MAC address of Ethernet Interface of a PC in C++

macaddress.cpp

#include <stdio.h>
#include <Windows.h>
#include <Iphlpapi.h>
#include <Assert.h>
#include <string>

#pragma comment(lib, "iphlpapi.lib")

char* getMAC();

int main(){ 
  char* pMac = getMAC();
  system("pause");
  free(pMac);
}
string gMAC() {
  PIP_ADAPTER_INFO AdapterInfo;
  DWORD dwBufLen = sizeof(IP_ADAPTER_INFO);
  char *mac_addr = (char*)malloc(18);

  AdapterInfo = (IP_ADAPTER_INFO *) malloc(sizeof(IP_ADAPTER_INFO));
  if (AdapterInfo == NULL) {
    printf("Error allocating memory needed to call GetAdaptersinfo\n");
    free(mac_addr);
    return NULL; // it is safe to call free(NULL)
  }

  // Make an initial call to GetAdaptersInfo to get the necessary size into the dwBufLen variable
  if (GetAdaptersInfo(AdapterInfo, &dwBufLen) == ERROR_BUFFER_OVERFLOW) {
    free(AdapterInfo);
    AdapterInfo = (IP_ADAPTER_INFO *) malloc(dwBufLen);
    if (AdapterInfo == NULL) {
      printf("Error allocating memory needed to call GetAdaptersinfo\n");
      free(mac_addr);
      return NULL;
    }
  }

  if (GetAdaptersInfo(AdapterInfo, &dwBufLen) == NO_ERROR) {
    // Contains pointer to current adapter info
    PIP_ADAPTER_INFO pAdapterInfo = AdapterInfo;
    do {
      // technically should look at pAdapterInfo->AddressLength
      //   and not assume it is 6.
      sprintf(mac_addr, "%02X:%02X:%02X:%02X:%02X:%02X",
        pAdapterInfo->Address[0], pAdapterInfo->Address[1],
        pAdapterInfo->Address[2], pAdapterInfo->Address[3],
        pAdapterInfo->Address[4], pAdapterInfo->Address[5]);
      printf("Address: %s, mac: %s\n", pAdapterInfo->IpAddressList.IpAddress.String, mac_addr);
      // print them all, return the last one.
      // return mac_addr;

      printf("\n");
      pAdapterInfo = pAdapterInfo->Next;        
    } while(pAdapterInfo);                        
  }
  free(AdapterInfo);
  return mac_addr; // caller must free.
}