How can I write into and read from clipboard?

[bona]

Suppose I want to pass a complex structure from one function to another, but I can't use pointers (or references).
How it can be done just using clipboard?

[Vlatko]

To put some data in the clipboard use the SetClipboardData API. Unfortunately i don't have an example right now, but here is some info:

SetClipboardData
The SetClipboardData function places data on the clipboard in a specified clipboard format. The window must be the current clipboard owner, and the application must have called the OpenClipboard function. (When responding to the WM_RENDERFORMAT and WM_RENDERALLFORMATS messages, the clipboard owner must not call OpenClipboard before calling SetClipboardData.) 

HANDLE SetClipboardData(
  UINT uFormat, // clipboard format
  HANDLE hMem   // data handle
);
 
Parameters
uFormat 
Specifies a clipboard format. This parameter can be a registered format or any of the standard clipboard formats. For more information, see Registered Clipboard Formats and Standard Clipboard Formats. 
hMem 
Handle to the data in the specified format. This parameter can be NULL, indicating that the window provides data in the specified clipboard format (renders the format) upon request. If a window delays rendering, it must process the WM_RENDERFORMAT and WM_RENDERALLFORMATS messages. 
After SetClipboardData is called, the system owns the object identified by the hMem parameter. The application can read the data, but must not free the handle or leave it locked. If the hMem parameter identifies a memory object, the object must have been allocated using the GlobalAlloc function with the GMEM_MOVEABLE and GMEM_DDESHARE flags. 

Return Values
If the function succeeds, the return value is the handle of the data.

If the function fails, the return value is NULL. To get extended error information, call GetLastError. 

Remarks
The uFormat parameter can identify a registered clipboard format, or it can be one of the standard clipboard formats. For more information, see Registered Clipboard Formats and Standard Clipboard Formats. 

The system performs implicit data format conversions between certain clipboard formats when an application calls the GetClipboardData function. For example, if the CF_OEMTEXT format is on the clipboard, a window can retrieve data in the CF_TEXT format. The format on the clipboard is converted to the requested format on demand. For more information, see Synthesized Clipboard Formats.

[Vlatko]

There is another way to pass complex structures

WM_COPYDATA
The WM_COPYDATA message is sent when an application passes data to another application. 

WM_COPYDATA 
wParam = (WPARAM) (HWND) hwnd;            // handle of sending window 
lParam = (LPARAM) (PCOPYDATASTRUCT) pcds; // pointer to structure with data 
 
Parameters
hwnd 
Handle to the window passing the data. 
pcds 
Pointer to a COPYDATASTRUCT structure that contains the data to be passed. 
Return Values
If the receiving application processes this message, it should return TRUE; otherwise, it should return FALSE. 

Remarks
An application must use theSendMessage function to send this message, not thePostMessage function. 

The data being passed must not contain pointers or other references to objects not accessible to the application receiving the data. 

While this message is being sent, the referenced data must not be changed by another thread of the sending process. 

The receiving application should consider the data read-only. The pcds parameter is valid only during the processing of the message. The receiving application should not free the memory referenced by pcds. If the receiving application must access the data after SendMessage returns, it must copy the data into a local buffer.

COPYDATASTRUCT
The COPYDATASTRUCT structure contains data to be passed to another application by the WM_COPYDATA message. 

typedef struct tagCOPYDATASTRUCT {  // cds 
    DWORD dwData; 
    DWORD cbData; 
    PVOID lpData; 
} COPYDATASTRUCT; 
 
Members
dwData 
Specifies up to 32 bits of data to be passed to the receiving application. 
cbData 
Specifies the size, in bytes, of the data pointed to by the lpData member. 
lpData 
Pointer to data to be passed to the receiving application. This member can be NULL.

This message can pass larger ammount of data to another app. It is not wise to use the clipboard because in the meantime another app can rewrite the content. I had an example of transfering data between apps (will have a look and post it).

[Vlatko]

Here is the example. It uses three different methods to pass data between apps.

Note: The comments are not in English, it uses MFC ('cos it is just an experiment).

[bona]

Thanks Vlatko,
Now I will have a look more careful at it.