Writing to a Mailslot

Writing to a mailslot is similar to writing to a standard disk file. The following code uses the CreateFile, WriteFile, and CloseHandle functions to put a short message in a mailslot. The message is broadcast to the mailslot server named "sample_mailslot" on the local computer. The code operates under the assumption that the mailslot server was already created.

#include <windows.h>
#include <stdio.h>

LPCTSTR SlotName = TEXT("\\\\.\\mailslot\\sample_mailslot");

BOOL WriteSlot(HANDLE hSlot, LPCTSTR lpszMessage)
{
 BOOL fResult; 
 DWORD cbWritten; 
 
 fResult = WriteFile(hSlot, 
 lpszMessage, 
 (DWORD) (lstrlen(lpszMessage)+1)*sizeof(TCHAR), 
 &cbWritten, 
 (LPOVERLAPPED) NULL); 
 
 if (!fResult) 
 { 
 printf("WriteFile failed with %d.\n", GetLastError()); 
 return FALSE; 
 } 
 
 printf("Slot written to successfully.\n"); 

 return TRUE;
}

int main()
{ 
 HANDLE hFile; 

 hFile = CreateFile(SlotName, 
 GENERIC_WRITE, 
 FILE_SHARE_READ,
 (LPSECURITY_ATTRIBUTES) NULL, 
 OPEN_EXISTING, 
 FILE_ATTRIBUTE_NORMAL, 
 (HANDLE) NULL); 
 
 if (hFile == INVALID_HANDLE_VALUE) 
 { 
 printf("CreateFile failed with %d.\n", GetLastError()); 
 return FALSE; 
 } 
 
 WriteSlot(hFile, TEXT("Message one for mailslot."));
 WriteSlot(hFile, TEXT("Message two for mailslot."));

 Sleep(5000);

 WriteSlot(hFile, TEXT("Message three for mailslot."));
 
 CloseHandle(hFile); 
 
 return TRUE;
}

The following is the output that is displayed when this example is run with the mailslot server shown in Reading from a Mailslot.

Slot written to successfully.
Slot written to successfully.
Slot written to successfully.