C / C++ / MFC

Rajesh R Subramanian wrote:

What are you doing answering C++ queries on a sunday, you addict.

Rajesh R Subramanian wrote:

Now, I'll wait for this book:

Writing ActiveX components with nothing but the 8086 assembler - by CPallini.

Rajesh R Subramanian wrote:

BTW, Jeff Glatt's series rocks.

CPallini wrote:

Unfortunately I can vote your post only once.

Jim Crafton wrote:

When I send a WM_SETFONT with a new font handle nothing happens

Mark Salsbery
Microsoft MVP - Visual C++

/* MultipleInstance.h */
 
class MultipleInstance {
 
public:
 
    MultipleInstance();
    ~MultipleInstance();
 
    static bool Active();
 
private:
 
    static bool                 _Active;
 
    static bool                 _Initialized;
    static HANDLE               _Handle;
    static MultipleInstance     *_Instance;
 
};
 
/* MultipleInstance.cpp */
 
static MultipleInstance _MultipleInstance;
 
bool                MultipleInstance::_Active       = false;
 
bool                MultipleInstance::_Initialized  = false;
HANDLE              MultipleInstance::_Handle       = NULL;
MultipleInstance    *MultipleInstance::_Instance    = &_MultipleInstance;
 
MultipleInstance::MultipleInstance()
{
    if ((!_Initialized) && (this == _Instance)) {
 
        // create security descriptor to let all users access the semaphore
 
        SECURITY_DESCRIPTOR security_descriptor = { 0 };
 
        InitializeSecurityDescriptor(&security_descriptor,
                                     SECURITY_DESCRIPTOR_REVISION);
 
        SetSecurityDescriptorDacl(&security_descriptor,TRUE,NULL,FALSE);
 
        // create semaphore
 
        SECURITY_ATTRIBUTES security_attributes = { 0 };
 
        security_attributes.nLength              = sizeof(security_attributes);
        security_attributes.lpSecurityDescriptor = &security_descriptor;
        security_attributes.bInheritHandle       = FALSE;
 
        SetLastError(0);
 
        _Handle = ::CreateSemaphore(&security_attributes,0,1,
                                    _T("Global\\InstanceSemaphore"));
                                    /* change "InstanceSemaphore" to your desired name */
 
        if (GetLastError() == ERROR_ALREADY_EXISTS) {
            _Active = true;
        }
 
        _Initialized = true;
 
    }
}
 
MultipleInstance::~MultipleInstance()
{
    if (_Initialized && (this == _Instance)) {
 
        if (_Handle != INVALID_HANDLE_VALUE) &&
           (_Handle != NULL)) {
 
            CloseHandle(_Handle);
            _Handle = NULL;
 
        }
 
    }
}
 
bool MultipleInstance::Active()
{
    return _Active;
}