DLL:Example:Windows

// The myPuts function writes a null-terminated string to
// the standard output device.

// The export mechanism used here is the __declspec(export)
// method supported by Microsoft Visual Studio, but any
// other export method supported by your development
// environment may be substituted.


#include <windows.h>

#define EOF (-1)

#ifdef __cplusplus    // If used by C++ code, 
extern "C" {          // we need to export the C interface
#endif

__declspec(dllexport) int __cdecl myPuts(LPWSTR lpszMsg)
{
    DWORD cchWritten;
    HANDLE hConout;
    BOOL fRet;

    // Get a handle to the console output device.

    hConout = CreateFileW(L"CONOUT$",
                         GENERIC_WRITE,
                         FILE_SHARE_WRITE,
                         NULL,
                         OPEN_EXISTING,
                         FILE_ATTRIBUTE_NORMAL,
                         NULL);

    if (INVALID_HANDLE_VALUE == hConout)
        return EOF;

    // Write a null-terminated string to the console output device.

    while (*lpszMsg != L'\0')
    {
        fRet = WriteConsole(hConout, lpszMsg, 1, &cchWritten, NULL);
        if( (FALSE == fRet) || (1 != cchWritten) )
            return EOF;
        lpszMsg++;
    }
    return 1;
}

#ifdef __cplusplus
}
#endif

#include <windows.h> 

extern "C" int __cdecl myPuts(LPWSTR);   // a function from a DLL

int main(VOID) 
{ 
    int Ret = 1;

    Ret = myPuts(L"Message sent to the DLL function\n"); 
    return Ret;
}

// A simple program that uses LoadLibrary and 
// GetProcAddress to access myPuts from Myputs.dll. 

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

typedef int (__cdecl *MYPROC)(LPWSTR); 

int main( void ) 
{ 
    HINSTANCE hinstLib; 
    MYPROC ProcAdd; 
    BOOL fFreeResult, fRunTimeLinkSuccess = FALSE; 

    // Get a handle to the DLL module.

    hinstLib = LoadLibrary(TEXT("MyPuts.dll")); 

    // If the handle is valid, try to get the function address.

    if (hinstLib != NULL) 
    { 
        ProcAdd = (MYPROC) GetProcAddress(hinstLib, "myPuts"); 

        // If the function address is valid, call the function.

        if (NULL != ProcAdd) 
        {
            fRunTimeLinkSuccess = TRUE;
            (ProcAdd) (L"Message sent to the DLL function\n"); 
        }
        // Free the DLL module.

        fFreeResult = FreeLibrary(hinstLib); 
    } 

    // If unable to call the DLL function, use an alternative.
    if (! fRunTimeLinkSuccess) 
        printf("Message printed from executable\n"); 

    return 0;

}

// The DLL code

#include <windows.h> 
#include <memory.h> 

#define SHMEMSIZE 4096 

static LPVOID lpvMem = NULL;      // pointer to shared memory
static HANDLE hMapObject = NULL;  // handle to file mapping

// The DLL entry-point function sets up shared memory using a 
// named file-mapping object. 

BOOL WINAPI DllMain(HINSTANCE hinstDLL,  // DLL module handle
    DWORD fdwReason,              // reason called 
    LPVOID lpvReserved)           // reserved 
{ 
    BOOL fInit, fIgnore; 

    switch (fdwReason) 
    { 
        // DLL load due to process initialization or LoadLibrary

          case DLL_PROCESS_ATTACH: 

            // Create a named file mapping object

            hMapObject = CreateFileMapping( 
                INVALID_HANDLE_VALUE,   // use paging file
                NULL,                   // default security attributes
                PAGE_READWRITE,         // read/write access
                0,                      // size: high 32-bits
                SHMEMSIZE,              // size: low 32-bits
                TEXT("dllmemfilemap")); // name of map object
            if (hMapObject == NULL) 
                return FALSE; 

            // The first process to attach initializes memory

            fInit = (GetLastError() != ERROR_ALREADY_EXISTS); 

            // Get a pointer to the file-mapped shared memory

            lpvMem = MapViewOfFile( 
                hMapObject,     // object to map view of
                FILE_MAP_WRITE, // read/write access
                0,              // high offset:  map from
                0,              // low offset:   beginning
                0);             // default: map entire file
            if (lpvMem == NULL) 
                return FALSE; 

            // Initialize memory if this is the first process

            if (fInit) 
                memset(lpvMem, '\0', SHMEMSIZE); 

            break; 

        // The attached process creates a new thread

        case DLL_THREAD_ATTACH: 
            break; 

        // The thread of the attached process terminates

        case DLL_THREAD_DETACH: 
            break; 

        // DLL unload due to process termination or FreeLibrary

        case DLL_PROCESS_DETACH: 

            // Unmap shared memory from the process's address space

            fIgnore = UnmapViewOfFile(lpvMem); 

            // Close the process's handle to the file-mapping object

            fIgnore = CloseHandle(hMapObject); 

            break; 

        default: 
          break; 
     } 

    return TRUE; 
    UNREFERENCED_PARAMETER(hinstDLL); 
    UNREFERENCED_PARAMETER(lpvReserved); 
} 

// The export mechanism used here is the __declspec(export)
// method supported by Microsoft Visual Studio, but any
// other export method supported by your development
// environment may be substituted.

#ifdef __cplusplus    // If used by C++ code, 
extern "C" {          // we need to export the C interface
#endif

// SetSharedMem sets the contents of the shared memory 

__declspec(dllexport) VOID __cdecl SetSharedMem(LPWSTR lpszBuf) 
{ 
    LPWSTR lpszTmp; 
    DWORD dwCount=1;

    // Get the address of the shared memory block

    lpszTmp = (LPWSTR) lpvMem; 

    // Copy the null-terminated string into shared memory

    while (*lpszBuf && dwCount<SHMEMSIZE) 
    {
        *lpszTmp++ = *lpszBuf++; 
        dwCount++;
    }
    *lpszTmp = '\0'; 
} 

// GetSharedMem gets the contents of the shared memory

__declspec(dllexport) VOID __cdecl GetSharedMem(LPWSTR lpszBuf, DWORD cchSize) 
{ 
    LPWSTR lpszTmp; 

    // Get the address of the shared memory block

    lpszTmp = (LPWSTR) lpvMem; 

    // Copy from shared memory into the caller's buffer

    while (*lpszTmp && --cchSize) 
        *lpszBuf++ = *lpszTmp++; 
    *lpszBuf = '\0'; 
}
#ifdef __cplusplus
}
#endif

// Parent process

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

extern "C" VOID __cdecl SetSharedMem(LPWSTR lpszBuf);

HANDLE CreateChildProcess(LPTSTR szCmdline) 
{ 
   PROCESS_INFORMATION piProcInfo; 
   STARTUPINFO siStartInfo;
   BOOL bFuncRetn = FALSE; 

// Set up members of the PROCESS_INFORMATION structure. 

   ZeroMemory( &piProcInfo, sizeof(PROCESS_INFORMATION) );

// Set up members of the STARTUPINFO structure. 

   ZeroMemory( &siStartInfo, sizeof(STARTUPINFO) );
   siStartInfo.cb = sizeof(STARTUPINFO); 

// Create the child process. 

   bFuncRetn = CreateProcess(NULL, 
      szCmdline,     // command line 
      NULL,          // process security attributes 
      NULL,          // primary thread security attributes 
      TRUE,          // handles are inherited 
      0,             // creation flags 
      NULL,          // use parent's environment 
      NULL,          // use parent's current directory 
      &siStartInfo,  // STARTUPINFO pointer 
      &piProcInfo);  // receives PROCESS_INFORMATION 

   if (bFuncRetn == 0) 
   {
      printf("CreateProcess failed (%)\n", GetLastError());
      return INVALID_HANDLE_VALUE;
   }
   else 
   {
      CloseHandle(piProcInfo.hThread);
      return piProcInfo.hProcess;
   }
}

int _tmain(int argc, TCHAR *argv[])
{
   HANDLE hProcess;

   if (argc == 1) 
   {
      printf("Please specify an input file");
      ExitProcess(0);
   }

   // Call the DLL function
   printf("\nProcess is writing to shared memory...\n\n");
   SetSharedMem(L"This is a test string");

   // Start the child process that will read the memory
   hProcess = CreateChildProcess(argv[1]);

   // Ensure this process is around until the child process terminates
   if (INVALID_HANDLE_VALUE != hProcess) 
   {
      WaitForSingleObject(hProcess, INFINITE);
      CloseHandle(hProcess);
   }
   return 0;
}

// Child process

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

extern "C" VOID __cdecl GetSharedMem(LPWSTR lpszBuf, DWORD cchSize);

int _tmain( void )
{
    WCHAR cBuf[MAX_PATH];

    GetSharedMem(cBuf, MAX_PATH);

    printf("Child process read from shared memory: %S\n", cBuf);

    return 0;
}

// The DLL code

#include <windows.h>

static DWORD dwTlsIndex; // address of shared memory

// DllMain() is the entry-point function for this DLL. 

BOOL WINAPI DllMain(HINSTANCE hinstDLL, // DLL module handle
    DWORD fdwReason,                    // reason called
    LPVOID lpvReserved)                 // reserved
{ 
    LPVOID lpvData; 
    BOOL fIgnore; 

    switch (fdwReason) 
    { 
        // The DLL is loading due to process 
        // initialization or a call to LoadLibrary. 

        case DLL_PROCESS_ATTACH: 

            // Allocate a TLS index.

            if ((dwTlsIndex = TlsAlloc()) == TLS_OUT_OF_INDEXES) 
                return FALSE; 

            // No break: Initialize the index for first thread.

        // The attached process creates a new thread. 

        case DLL_THREAD_ATTACH: 

            // Initialize the TLS index for this thread.

            lpvData = (LPVOID) LocalAlloc(LPTR, 256); 
            if (lpvData != NULL) 
                fIgnore = TlsSetValue(dwTlsIndex, lpvData); 

            break; 

        // The thread of the attached process terminates.

        case DLL_THREAD_DETACH: 

            // Release the allocated memory for this thread.

            lpvData = TlsGetValue(dwTlsIndex); 
            if (lpvData != NULL) 
                LocalFree((HLOCAL) lpvData); 

            break; 

        // DLL unload due to process termination or FreeLibrary. 

        case DLL_PROCESS_DETACH: 

            // Release the allocated memory for this thread.

            lpvData = TlsGetValue(dwTlsIndex); 
            if (lpvData != NULL) 
                LocalFree((HLOCAL) lpvData); 

            // Release the TLS index.

            TlsFree(dwTlsIndex); 
            break; 

        default: 
            break; 
    } 

    return TRUE; 
    UNREFERENCED_PARAMETER(hinstDLL); 
    UNREFERENCED_PARAMETER(lpvReserved); 
}

// The export mechanism used here is the __declspec(export)
// method supported by Microsoft Visual Studio, but any
// other export method supported by your development
// environment may be substituted.

#ifdef __cplusplus    // If used by C++ code, 
extern "C" {          // we need to export the C interface
#endif

__declspec(dllexport)
BOOL WINAPI StoreData(DWORD dw)
{
   LPVOID lpvData; 
   DWORD * pData;  // The stored memory pointer 

   lpvData = TlsGetValue(dwTlsIndex); 
   if (lpvData == NULL)
   {
      lpvData = (LPVOID) LocalAlloc(LPTR, 256); 
      if (lpvData == NULL) 
         return FALSE;
      if (!TlsSetValue(dwTlsIndex, lpvData))
         return FALSE;
   }

   pData = (DWORD *) lpvData; // Cast to my data type.
   // In this example, it is only a pointer to a DWORD
   // but it can be a structure pointer to contain more complicated data.

   (*pData) = dw;
   return TRUE;
}

__declspec(dllexport)
BOOL WINAPI GetData(DWORD *pdw)
{
   LPVOID lpvData; 
   DWORD * pData;  // The stored memory pointer 

   lpvData = TlsGetValue(dwTlsIndex); 
   if (lpvData == NULL)
      return FALSE;

   pData = (DWORD *) lpvData;
   (*pdw) = (*pData);
   return TRUE;
}
#ifdef __cplusplus
}
#endif

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

#define THREADCOUNT 4 
#define DLL_NAME TEXT("testdll")

VOID ErrorExit(LPSTR); 

extern "C" BOOL WINAPI StoreData(DWORD dw);
extern "C" BOOL WINAPI GetData(DWORD *pdw);

DWORD WINAPI ThreadFunc(VOID) 
{   
   int i;

   if(!StoreData(GetCurrentThreadId()))
      ErrorExit("StoreData error");

   for(i=0; i<THREADCOUNT; i++)
   {
      DWORD dwOut;
      if(!GetData(&dwOut))
         ErrorExit("GetData error");
      if( dwOut != GetCurrentThreadId())
         printf("thread %d: data is incorrect (%d)\n", GetCurrentThreadId(), dwOut);
      else printf("thread %d: data is correct\n", GetCurrentThreadId());
      Sleep(0);
   }
   return 0; 
} 

int main(VOID) 
{ 
   DWORD IDThread; 
   HANDLE hThread[THREADCOUNT]; 
   int i; 
   HMODULE hm;

// Load the DLL

   hm = LoadLibrary(DLL_NAME);
   if(!hm)
   {
      ErrorExit("DLL failed to load");
   }

// Create multiple threads. 

   for (i = 0; i < THREADCOUNT; i++) 
   { 
      hThread[i] = CreateThread(NULL, // default security attributes 
         0,                           // use default stack size 
         (LPTHREAD_START_ROUTINE) ThreadFunc, // thread function 
         NULL,                    // no thread function argument 
         0,                       // use default creation flags 
         &IDThread);              // returns thread identifier 

   // Check the return value for success. 
      if (hThread[i] == NULL) 
         ErrorExit("CreateThread error\n"); 
   } 

   WaitForMultipleObjects(THREADCOUNT, hThread, TRUE, INFINITE); 

   FreeLibrary(hm);

   return 0; 
} 

VOID ErrorExit (LPSTR lpszMessage) 
{ 
   fprintf(stderr, "%s\n", lpszMessage); 
   ExitProcess(0); 
}