DevelopersVoice.com

Q: How do I choose a font size to exactly fit a string in a given rectangle?
A: Choosing font width and height by calculating the rectangle width and height will not solve this problem perfectly. This will only give a font which approximately fit in the rectangle, since characters are of different widths.

In this method, calculating the font size is done in two steps. First, rough font width and height are calculated from rectangle dimensions. This font is then selected for the display device context and exact width and height is determined. From this actual font dimensions, required font dimensions are calculated by proportionately sizing the font.

When you output multiple lines, some space is left between characters in subsequent lines ('tmExternalLeading' of 'TEXTMETRIC' structure). While evaluating the font size, this is also taken into account.

The method is wrapped into a function 'TextOut()'. This is similar to the SDK function 'TextOut', but differs in the type of arguments. First argument is handle to device context, similar to the SDK function. Second and third arguments are pointer to the rectangle and character array respectively. Here is the code, with comments sprinkled liberally:

Result is shown in the attached image. Rectangle is shown in gray shade over which the string is output in transparent mode.

Note: Most of the material in this article is taken from codeguru.com

Q: How to convert between ANSI and UNICODE strings?
A:
The quick and dirty way

This way of working is correct for codepages that are single-byte and Unicode strings that are UCS2. This applies to most cases, but if your program should run correctly on Japanese, Chinese, Taiwanese and other systems which have DBCS codepages then use the "correct way" described further below.

ANSI to UNICODE:

The conversion is done using the 'MultiByteToWideChar()'

UNICODE to ANSI:

The UNICODE string mostly is returned by some COM function, like this one:

The conversion is done using the 'WideCharToMultiByte()' function:

The correct way

If you want to handle DBCS codepages and UTF-16 Unicode strings then you should do things this way. The idea is to call 'MultiByteToWideChar()' resp. 'WideCharToMultiByte()' twice. First you get the length of the result, then you allocate the resulting string and call it again to convert.

ANSI to Unicode

Unicode to ANSI

Note: Most of the material in this article is taken from codeguru.com

Q: How can I write data to the registry?

A: To open the registry key use the function RegOpenKeyEx. To write a vaule from registry use the function RegSetValueEx.

Note: Most of the material in this article is taken from codeguru.com

Q: How can I read data from the registry?

A: To open the registry key use the function RegOpenKeyEx. To read a vaule from registry use the function RegQueryValueEx.

Q: The RegQueryValueEx function returns an error code 234 (ERROR_MORE_DATA) that means "more data is available". How many bytes must be allocated for value buffer to assure this error does not appear anymore?

A: To find the necessary buffer size, call 'RegQueryValueEx()' with a 'NULL' value in 'lpData' parameter. After return, the variable pointed by 'lpcbData' will contain the size of the data. Allocate the buffer 'lpData' then call 'RegQueryValueEx()' again:

Note: Most of the material in this article is taken from codeguru.com

Q: How to use member functions as thread functions?
A: While trying to use member functions of a class as thread functions the compiler might complain with some kind of error like

The problem is that every thread function has its own prototype, which determines the parameters that gets passed from the operating system to it.

In C++ every member function has a hidden parameter - the so-called 'this' pointer which will be automatically passed to the function. C++ is able to associate a function with a particular instance of an object by means of the 'this' pointer. Member functions access member variables through the 'this' pointer...

This code will be compiled as

The operating system does not call thread functions through objects therefore it cannot handle the automatically added 'this' pointer... To get member functions working as thread routines you need to tell the compiler explicitly not to expect a 'this' pointer. To avoid the automatic 'this' pointer you have two possibilities:

• Non-member functions
• Static member functions

Non-member functions are not part of a class and therefore do not have a 'this' pointer. Static member functions do not receive a this' pointer either...thus, if you want to use a member function as a thread routine you need to declare it as 'static'...

More information can be found here and here.

Note: Most of the material in this article is taken from codeguru.com

Q: How to end a thread?
A: There are different ways depending whether the thread will be ended from inside or outside. For ending a thread from inside the function 'ExitThread()' can be used.

This will end the actual thread. It is the preferred method to end a thread. This function will also be called implicitly while returning from the thread procedure and provides a clean shutdown of the thread.

To end a thread from outside there exist also two general possibilities. To provide a clean exit of the thread an event can be set which was passed as a thread parameter and which is frequently checked by the thread procedure.

If the approach described above is not possible for several reasons (e.g. a lengthy database query is performed) then the thread can be forced to exit by a call to 'TerminateThread()'.

'hThread' is the handle of the thread which can be obtained by use of any of the functions described in 'How to create a worker thread?'. On Windows NT, Windows 2000 and Windows XP systems, the handle must have 'THREAD_TERMINATE' access.

'TerminateThread()' has some drawbacks which should be considered. It causes the thread to exit. When this occurs, the thread does not have the chance to execute any user-mode code any longer. DLLs attached to the thread are not notified that the thread is terminating.

Additional information is provided by the MSDN:

Note: Most of the material in this article is taken from codeguru.com

Q: How to end a thread?
A: There are different ways depending whether the thread will be ended from inside or outside. For ending a thread from inside the function 'ExitThread()' can be used.

This will end the actual thread. It is the preferred method to end a thread. This function will also be called implicitly while returning from the thread procedure and provides a clean shutdown of the thread.

To end a thread from outside there exist also two general possibilities. To provide a clean exit of the thread an event can be set which was passed as a thread parameter and which is frequently checked by the thread procedure.

If the approach described above is not possible for several reasons (e.g. a lengthy database query is performed) then the thread can be forced to exit by a call to 'TerminateThread()'.

'hThread' is the handle of the thread which can be obtained by use of any of the functions described in 'How to create a worker thread?'. On Windows NT, Windows 2000 and Windows XP systems, the handle must have 'THREAD_TERMINATE' access.

'TerminateThread()' has some drawbacks which should be considered. It causes the thread to exit. When this occurs, the thread does not have the chance to execute any user-mode code any longer. DLLs attached to the thread are not notified that the thread is terminating.

Additional information is provided by the MSDN:

Note: Most of the material in this article is taken from codeguru.com

Q: How to create a worker thread?
A: There are several ways to create a worker thread:

• '_beginthread()' (C run-time library)
• '_beginthreadex()' (C run-time library)
• 'CreateThread()' (Win32 API)
• 'CreateRemoteThread()' (Win32 API)
• 'AfxBeginThread()' (MFC)

The following samples will show the creation of a thread using the three functions '_beginthreadex()', 'CreateThread()' and 'AfxBeginThread()'.

1. '_beginthreadex()'
   
   class CFoo
   {
   public:
   CFoo()
   {
   m_uiThreadID = 0;
   m_ulThreadHandle = 0;
   }
   bool Create()
   {
   m_ulThreadHandle = _beginthreadex(0,
   0,
   ThreadFunc,
   this,
   0,
   &m_uiThreadID);
   if(!m_ulThreadHandle)
   {
   // Could not create thread
   return false;
   }
   return true;
   }
   private:
   unsigned int m_uiThreadID;
   unsigned long m_ulThreadHandle;
   static unsigned int __stdcall ThreadFunc(void *pvParam);
   };
2. 'AfxBeginThread()'
   
   class CMyDialog : public CDialog
   {
   public:
   CMyDialog(CWnd* pParent = NULL)
   : CDialog(CMyDialog::IDD, pParent)
   {
   m_pThread = 0;
   }
   bool Create()
   {
   m_pThread = AfxBeginThread(ThreadFunc, this);
   if(!m_pThread)
   {
   // Could not create thread
   return false;
   }
   return true;
   }
   private:
   CWinThread *m_pThread;
   static UINT ThreadFunc(LPVOID pvParam);
   };
   

    

Note: Most of the material in this article is taken from codeguru.com

Processes: How can I wait until a process ends?

Q: How can I wait until a process ends?
A: Depending on the method chosen for creating the process, waiting until it is finished is pretty easy to implement. 'CreateProcess()' provides handles both to the process and its primary thread within the 'PROCESS_INFORMATION' structure. The process handle can be used to wait for termination of the process:

'ShellExecuteEx()' provides only a handle to the process but unfortunately it is not guaranteed and is depending on several options you can set within the 'SHELLEXECUTEINFO' structure. For any other method used to create the process a handle to the process needs to be obtained first.

Note: Most of the material in this article is taken from codeguru.com

Q: How can I start a process ?
A: There are several ways to start a process:

• 'system()' family (C run-time library - ANSI ('system()') or Win NT ('_wsystem()'))
• '_exec()' family (C run-time library - Win 95, Win NT)
• '_spawn()' family (C run-time library - Win 95, Win NT)
• 'WinExec()' (Win32 API)
• 'ShellExecute()' (Shell API)
• 'ShellExecuteEx()' (Shell API)
• 'CreateProcess()' (Win32 API)
• 'CreateProcessAsUser()' (Win32 API)
• 'CreateProcessWithLogonW()' (Win32 API)

Most common are 'ShellExecute()', ShellExecuteEx()' and 'CreateProcess()'. Note that 'WinExec()' is provided only for compatibility with 16-bit Windows and should not be used any longer. The following examples will show how to display the text file 'c:\example.txt' in 'notepad.exe' using these three functions...

1. 'ShellExecute()'
   
   HINSTANCE hInst = ShellExecute(0,
   "open", // Operation to perform
   "c:\\windows\\notepad.exe", // Application name
   "c:\\example.txt", // Additional parameters
   0, // Default directory
   SW_SHOW);
   if(reinterpret_cast<int>(hInst) <= 32)
   {
   // Could not start application
   switch(reinterpret_cast<int>(hInst))
   {
   case 0:
   // The operating system is out of memory or resources.
   break;
   case ERROR_FILE_NOT_FOUND:
   // The specified file was not found.
   break;
   case ERROR_PATH_NOT_FOUND:
   // The specified path was not found.
   break;
   case ERROR_BAD_FORMAT:
   // The .exe file is invalid (non-Microsoft Win32 .exe or error in .exe image).
   break;
   case SE_ERR_ACCESSDENIED:
   // The operating system denied access to the specified file.
   break;
   case SE_ERR_ASSOCINCOMPLETE:
   // The file name association is incomplete or invalid.
   break;
   case SE_ERR_DDEBUSY:
   // The Dynamic Data Exchange (DDE) transaction could not be completed because
   // other DDE transactions were being processed.
   break;
   case SE_ERR_DDEFAIL:
   // The DDE transaction failed.
   break;
   case SE_ERR_DDETIMEOUT:
   // The DDE transaction could not be completed because the request timed out.
   break;
   case SE_ERR_DLLNOTFOUND:
   // The specified dynamic-link library (DLL) was not found.
   
   case SE_ERR_FNF:
   // The specified file was not found.
   break;
   case SE_ERR_NOASSOC:
   // There is no application associated with the given file name extension.
   // This error will also be returned if you attempt to print a file that is
   // not printable.
   break;
   case SE_ERR_OOM:
   // There was not enough memory to complete the operation.
   break;
   case SE_ERR_PNF:
   // The specified path was not found.
   break;
   case SE_ERR_SHARE:
   // A sharing violation occurred.
   break;
   }
   }
2. 'ShellExecuteEx()'
   
   SHELLEXECUTEINFO ExecuteInfo;
   memset(&ExecuteInfo, 0, sizeof(ExecuteInfo));
   ExecuteInfo.cbSize = sizeof(ExecuteInfo);
   ExecuteInfo.fMask = 0;
   ExecuteInfo.hwnd = 0;
   ExecuteInfo.lpVerb = "open"; // Operation to perform
   ExecuteInfo.lpFile = "c:\\windows\\notepad.exe"; // Application name
   ExecuteInfo.lpParameters = "c:\\example.txt"; // Additional parameters
   ExecuteInfo.lpDirectory = 0; // Default directory
   ExecuteInfo.nShow = SW_SHOW;
   ExecuteInfo.hInstApp = 0;
   if(ShellExecuteEx(&ExecuteInfo) == FALSE)
   // Could not start application -> call 'GetLastError()'
3. 'CreateProcess()'
   
   STARTUPINFO siStartupInfo;
   PROCESS_INFORMATION piProcessInfo;
   memset(&siStartupInfo, 0, sizeof(siStartupInfo));
   memset(&piProcessInfo, 0, sizeof(piProcessInfo));
   siStartupInfo.cb = sizeof(siStartupInfo);
   if(CreateProcess("c:\\windows\\notepad.exe", // Application name
   " example.txt", // Application arguments
   0,
   0,
   FALSE,
   CREATE_DEFAULT_ERROR_MODE,
   0,
   0, // Working directory
   &siStartupInfo,
   &piProcessInfo) == FALSE)
   // Could not start application -> call 'GetLastError()'
   In general 'ShellExecuteEx()' and even 'CreateProcess()' provides more controlling features of the application to start and its termination.

Note: Most of the material in this article is taken from codeguru.com