RasEnumDevicesA function (ras.h)

The RasEnumDevices function returns the name and type of all available RAS-capable devices.


DWORD RasEnumDevicesA(
  [in]      LPRASDEVINFOA unnamedParam1,
  [in, out] LPDWORD       unnamedParam2,
  [out]     LPDWORD       unnamedParam3


[in] unnamedParam1

Pointer to a buffer that receives an array of RASDEVINFO structures, one for each RAS-capable device. Before calling the function, set the dwSize member of the first RASDEVINFO structure in the buffer to sizeof(RASDEVINFO) to identify the version of the structure.

[in, out] unnamedParam2

Pointer to a variable that, on input, contains the size, in bytes, of the lpRasDevInfo buffer.

On output, the function sets this variable to the number of bytes required to enumerate the devices.


To determine the required buffer size, call RasEnumDevices with lpRasDevInfo set to NULL. The variable pointed to by lpcb should be set to zero. The function will return the required buffer size in lpcb and an error code of ERROR_BUFFER_TOO_SMALL.


[out] unnamedParam3

Pointer to a variable that receives the number of RASDEVINFO structures written to the lpRasDevInfo buffer.

Return value

If the function succeeds, the return value is ERROR_SUCCESS.

If the function fails, the return value is one of the following error codes or a value from Routing and Remote Access Error Codes or Winerror.h.

Value Meaning
The lpRasDevInfo buffer is not large enough. The lpcb parameter is less than the dwSize member in the lpRasDevInfo parameter which should be set prior to calling the function. The function returns the required buffer size in the variable pointed to by lpcb.
Indicates insufficient memory. The lpRasDevInfo parameter is non-NULL, the lpcb parameter is non-NULL and an internal memory allocation failed. This is possibly due to a low-memory condition.
Indicates an invalid parameter value. The lpcb parameter is NULL or the lpcDevices parameter is NULL.
The address or buffer specified by lpRasDevInfo is invalid. The dwSize member of the lpRasDevInfo parameter does not equal sizeof(RASDEVINFO).


The following sample code enumerates the devices on the current machine. The code initially calls RasEnumDevices with a lpRasDevInfo parameter of NULL, to obtain the size of the buffer that should be passed in. The code also sets the dwSize member of the first RASDEVINFO structure to sizeof(RASDEVINFO) to specify the version of the structure.

#include <windows.h>
#include <stdio.h>
#include "ras.h"
#include "raserror.h"
#pragma comment(lib, "rasapi32.lib")

DWORD __cdecl wmain(){

    DWORD dwCb = 0;
    DWORD dwDevices = 0;
    // Call RasEnumDevices with lpRasDevInfo = NULL. dwCb is returned with the required buffer size and 
    // a return code of ERROR_BUFFER_TOO_SMALL
    dwRet = RasEnumDevices(lpRasDevInfo, &dwCb, &dwDevices);

    if (dwRet == ERROR_BUFFER_TOO_SMALL){
        // Allocate the memory needed for the array of RAS structure(s).
        lpRasDevInfo = (LPRASDEVINFO) HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, dwCb);
        if (lpRasDevInfo == NULL){
            wprintf(L"HeapAlloc failed!\n");
            return 0;
        // The first RASDEVINFO structure in the array must contain the structure size
        lpRasDevInfo[0].dwSize = sizeof(RASDEVINFO);
        // Call RasEnumDevices to enumerate RAS devices
        dwRet = RasEnumDevices(lpRasDevInfo, &dwCb, &dwDevices);

        // If successful, print the names of the RAS devices
        if (ERROR_SUCCESS == dwRet){
            wprintf(L"The following RAS devices were found:\n");
            for (DWORD i = 0; i < dwDevices; i++){
                         wprintf(L"%s\n", lpRasDevInfo[i].szDeviceName);
        //Deallocate memory for the connection buffer
        HeapFree(GetProcessHeap(), 0, lpRasDevInfo);
        lpRasDevInfo = NULL;
        return 0;

    // There was either a problem with RAS or there are no RAS devices to enumerate    
    if(dwDevices >= 1){
        wprintf(L"The operation failed to acquire the buffer size.\n");
        wprintf(L"There were no RAS devices found.\n");

    return 0;


The ras.h header defines RasEnumDevices as an alias which automatically selects the ANSI or Unicode version of this function based on the definition of the UNICODE preprocessor constant. Mixing usage of the encoding-neutral alias with code that not encoding-neutral can lead to mismatches that result in compilation or runtime errors. For more information, see Conventions for Function Prototypes.


Minimum supported client Windows 2000 Professional [desktop apps only]
Minimum supported server Windows 2000 Server [desktop apps only]
Target Platform Windows
Header ras.h
Library Rasapi32.lib
DLL Rasapi32.dll

See also


Remote Access Service (RAS) Overview

Remote Access Service Functions