Ports via NativeCOM to the NT system. How does your application know which ports have been defined in the system? The answer: the Windows NT Registry.

The Windows NT registry's hardware devicemap contains the COM ports defined in the system. You can see this key using regedit or regedt32. For example:

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

In this case, there are two serial ports built in to the machine, and at least three NativeCOM serial ports defined (these are identified as "RcsmSerialn"). The only part your application needs to know about is the "value" of the registry entries ("COM3" for instance)

The following "C" code example illustrates how your application might traverse the Registry to find this information so it can display it for your user.

//
// 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]);
}
}

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