HKEY_LOCAL_MACHINE
    HARDWARE
        DEVICEMAP
            SERIALCOMM
                Serial0      REG_SZ  COM1
                Serial1      REG_SZ  COM2
                Rcs0Serial3  REG_SZ  COM3
                Rcs0Serial4  REG_SZ  COM4

//
// Example program to retrieve all the COM port names from the NT Registry
//
#include 
#include 

//
// This example stores the found COM names in this array.  Your application
// may have some other place it wants to have COM names stored.
//
char CommList[256][64];

int GetCommList(void) 
{
    DWORD   resVal;
    HKEY    hSerialCommKey = NULL;
    DWORD   i, status;
    DWORD   keyType, nameBufSize, dataBufSize;
    UCHAR   valueKeyName[64], valueKeyData[64];

//
    // First - Get access to the registry key we need
    //
    resVal = RegOpenKeyEx(HKEY_LOCAL_MACHINE, 
                           "HARDWARE\\DEVICEMAP\\SERIALCOMM",
                           0, KEY_READ, &hSerialCommKey);

    //
    // If successful, read all the registry entries under this key

if( resVal == ERROR_SUCCESS ) {
        for( i = 0;; i++ ) {
            nameBufSize = dataBufSize = 64;
            status = RegEnumValue(
                        hSerialCommKey,
                        i,
                        (CHAR *)valueKeyName,
                        &nameBufSize,
                        NULL,
                        &keyType,
                        (UCHAR *)valueKeyData,
                        &dataBufSize
                        );

//
            // If we got something, the value of the key is the COM name
            //   otherwise we've come to the end of the list.
            //
            if (status == ERROR_SUCCESS) 
                strcpy(CommList[i], (const char *)valueKeyData);
            else
                break;
        

}
        //
        // Done, close down the registry before returning
        //
        RegCloseKey(hSerialCommKey);
        //
        // And return the number we found
        //
        return i;
     }
     else
         return -1;    // Return -1 as an error if we can't access the registry
}

void main(void) {
    DWORD count;
    DWORD i;

    if((count = GetCommList()) >= 0) {
        printf("Found %d COM ports\n", count);
        for (i = 0; i < count; i++)
            printf("%s\n", CommList[i]);
    }
}