SCardLocateCardsW function (winscard.h)

Article
02/09/2023

The SCardLocateCards function searches the readers listed in the rgReaderStates parameter for a card with an ATR string that matches one of the card names specified in mszCards, returning immediately with the result.

Syntax

LONG SCardLocateCardsW(
  [in]      SCARDCONTEXT         hContext,
  [in]      LPCWSTR              mszCards,
  [in, out] LPSCARD_READERSTATEW rgReaderStates,
  [in]      DWORD                cReaders
);

Parameters

[in] hContext

A handle that identifies the resource manager context. The resource manager context is set by a previous call to SCardEstablishContext.

[in] mszCards

A multiple string that contains the names of the cards to search for.

[in, out] rgReaderStates

An array of SCARD_READERSTATE structures that, on input, specify the readers to search and that, on output, receives the result.

[in] cReaders

The number of elements in the rgReaderStates array.

Return value

This function returns different values depending on whether it succeeds or fails.

Return code	Description
Success	SCARD_S_SUCCESS.
Failure	An error code. For more information, see Smart Card Return Values.

Remarks

This service is especially useful when used in conjunction with SCardGetStatusChange. If no matching cards are found by means of SCardLocateCards, the calling application may use SCardGetStatusChange to wait for card availability changes.

The SCardLocateCards function is a smart card tracking function. For more information on other tracking functions, see Smart Card Tracking Functions.

Calling this function should be done outside of a transaction. If an application begins a transaction with the SCardBeginTransaction function and then calls this function, it resets the hCard parameter (of type SCARDHANDLE) of the SCardBeginTransaction function.

Windows Server 2008 R2 and Windows 7: Calling this function within a transaction could result in your computer becoming unresponsive.

Windows Server 2008, Windows Vista, Windows Server 2003 and Windows XP: Not applicable.

Examples

The following example shows locating smart cards.

// Copyright (C) Microsoft. All rights reserved. 
#include <stdio.h>
#include <winscard.h>
#include <tchar.h>
#pragma comment(lib, "winscard.lib")

HRESULT __cdecl main()
{
HRESULT           hr = S_OK;
LPTSTR            szReaders, szRdr;
DWORD             cchReaders = SCARD_AUTOALLOCATE;
DWORD             dwI, dwRdrCount;
SCARD_READERSTATE rgscState[MAXIMUM_SMARTCARD_READERS];
TCHAR             szCard[MAX_PATH];
SCARDCONTEXT      hSC;
LONG              lReturn;

// Establish the card to watch for.
// Multiple cards can be looked for, but
// this sample looks for only one card.
_tcscat_s ( szCard, MAX_PATH * sizeof(TCHAR), TEXT("GemSAFE"));
szCard[lstrlen(szCard) + 1] = 0;  // Double trailing zero.

// Establish a context.
lReturn = SCardEstablishContext(SCARD_SCOPE_USER,
                                NULL,
                                NULL,
                                &hSC );
if ( SCARD_S_SUCCESS != lReturn )
{
    printf("Failed SCardEstablishContext\n");
    exit(1);
}

// Determine which readers are available.
lReturn = SCardListReaders(hSC,
                           NULL,
                           (LPTSTR)&szReaders,
                           &cchReaders );
if ( SCARD_S_SUCCESS != lReturn )
{
    printf("Failed SCardListReaders\n");
    exit(1);
}
// Place the readers into the state array.
szRdr = szReaders;
for ( dwI = 0; dwI < MAXIMUM_SMARTCARD_READERS; dwI++ )
{
    if ( 0 == *szRdr )
        break;
    rgscState[dwI].szReader = szRdr;
    rgscState[dwI].dwCurrentState = SCARD_STATE_UNAWARE;
    szRdr += lstrlen(szRdr) + 1;
}
dwRdrCount = dwI;

// If any readers are available, proceed.
if ( 0 != dwRdrCount )
{
  for (;;)
  { 
    // Look for the card.
    lReturn = SCardLocateCards(hSC,
                               szCard,
                               rgscState,
                               dwRdrCount );
    if ( SCARD_S_SUCCESS != lReturn )
    {
        printf("Failed SCardLocateCards\n");
        exit(1);
    }

    // Look through the array of readers.
    for ( dwI=0; dwI < dwRdrCount; dwI++)
    {
        if ( 0 != ( SCARD_STATE_ATRMATCH & 
                    rgscState[dwI].dwEventState))
        {
           _tprintf( TEXT("Card '%s' found in reader '%s'.\n"),
                     szCard,
                     rgscState[dwI].szReader );
            SCardFreeMemory( hSC,
                             szReaders );
            return 0;  // Context will be release automatically.
        }
        // Update the state.
        rgscState[dwI].dwCurrentState = rgscState[dwI].dwEventState;
    }

  // Card not found yet; wait until there is a change.
  lReturn = SCardGetStatusChange(hSC,
                                 INFINITE, // infinite wait
                                 rgscState,
                                 dwRdrCount );
  if ( SCARD_S_SUCCESS != lReturn )
  {
    printf("Failed SCardGetStatusChange\n");
    exit(1);
  }
 }  // for (;;)
}
else
    printf("No readers available\n");

// Release the context.
lReturn = SCardReleaseContext(hSC);
if ( SCARD_S_SUCCESS != lReturn )
{
    printf("Failed SCardReleaseContext\n");
    exit(1);
}

SCardFreeMemory( hSC,
                 szReaders );

return hr;
}

Note

The winscard.h header defines SCardLocateCards as an alias that 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 is not encoding-neutral can lead to mismatches that result in compilation or runtime errors. For more information, see Conventions for Function Prototypes.

Requirements

Requirement	Value
Minimum supported client	Windows XP [desktop apps only]
Minimum supported server	Windows Server 2003 [desktop apps only]
Target Platform	Windows
Header	winscard.h
Library	Winscard.lib
DLL	Winscard.dll

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