mfc acombo box add string - windows

Question

HKEY hKey = 0;
DWORD dwType = REG_SZ;
TCHAR buf[255] = {0};
DWORD dwBufSize = sizeof(buf);
DWORD ret;
CComboBox m_portCombo;
if( RegOpenKeyEx( HKEY_LOCAL_MACHINE, TEXT("HARDWARE\\DEVICEMAP\\SERIALCOMM"), 0, KEY_QUERY_VALUE, &hKey ) == ERROR_SUCCESS )
{
if( RegQueryValueEx( hKey, TEXT("\\Device\\Serial0"), 0, &dwType, (LPBYTE)buf, &dwBufSize ) == ERROR_SUCCESS )
{
CString str = buf;
m_portCombo.AddString(str);
}
if( RegQueryValueEx( hKey, TEXT("\\Device\\Serial1"), 0, &dwType, (LPBYTE)buf, &dwBufSize ) == ERROR_SUCCESS )
{
CString str = buf;
}
if( RegQueryValueEx( hKey, TEXT("\\Device\\Serial2"), 0, &dwType, (LPBYTE)buf, &dwBufSize ) == ERROR_SUCCESS )
{
CString str = buf;
}
if( RegQueryValueEx( hKey, TEXT("\\Device\\Serial3"), 0, &dwType, (LPBYTE)buf, &dwBufSize ) == ERROR_SUCCESS )
{
CString str = buf;
}
}
First problem: i want to change the TEXT("\\Device\\Serial3") with something like TEXT("\\Device\\Serial",%i), so i can resume all that lines of code to a for loop.Is tehre a way to accomplish this?
Second problem: if i use the m_portCombo.AddString(str); i get an Debug Assertion Failed! error, and, of course, the combobox is not populated with that registry value. Why could that happen?

Answer 1

First Problem: Use the CString Format() function using %d for integer.
for (int i =0 ; i<10; i++)
{
CString szPath;
szPath.Format(TEXT("\\Device\\Serial%d"),i);
// ...
}
Second Problem:
There could be many reasons this would fail. Most likely of which would be having not created the combo box yet.(It needs a window handle before it can add strings) To figure out the cause of the debug assertion, click the "retry" button on the Debug Assertion Failed window and it should jump to the code which caused the assertion. For example it might be something like:
ASSERT(GetSafeHwnd()!=NULL);

Answer 2

Your combo box class won't be 'subclassed' until after the first DoDataExchange is called (and any attempt to use it before that happens will ASSERT). Either wait until the base class has run OnInitDialog or do something like this:
CComboBox * pcombo = static_cast<CComboBox*>(GetDlgItem( IDC_MYCOMBO ));
pcombo->AddString( szPath );
See #TheSteve's answer for string problem.