SCardListReadersA function (winscard.h)

Article
02/09/2023

The SCardListReaders function provides the list of readers within a set of named reader groups, eliminating duplicates.

The caller supplies a list of reader groups, and receives the list of readers within the named groups. Unrecognized group names are ignored. This function only returns readers within the named groups that are currently attached to the system and available for use.

Syntax

LONG SCardListReadersA(
  [in]           SCARDCONTEXT hContext,
  [in, optional] LPCSTR       mszGroups,
  [out]          LPSTR        mszReaders,
  [in, out]      LPDWORD      pcchReaders
);

Parameters

[in] hContext

Handle that identifies the resource manager context for the query. The resource manager context can be set by a previous call to SCardEstablishContext.

If this parameter is set to NULL, the search for readers is not limited to any context.

[in, optional] mszGroups

Names of the reader groups defined to the system, as a multi-string. Use a NULL value to list all readers in the system (that is, the SCard$AllReaders group).

Value	Meaning
SCARD_ALL_READERS TEXT("SCard$AllReaders\000")	Group used when no group name is provided when listing readers. Returns a list of all readers, regardless of what group or groups the readers are in.
SCARD_DEFAULT_READERS TEXT("SCard$DefaultReaders\000")	Default group to which all readers are added when introduced into the system.
SCARD_LOCAL_READERS TEXT("SCard$LocalReaders\000")	Unused legacy value. This is an internally managed group that cannot be modified by using any reader group APIs. It is intended to be used for enumeration only.
SCARD_SYSTEM_READERS TEXT("SCard$SystemReaders\000")	Unused legacy value. This is an internally managed group that cannot be modified by using any reader group APIs. It is intended to be used for enumeration only.

[out] mszReaders

Multi-string that lists the card readers within the supplied reader groups. If this value is NULL, SCardListReaders ignores the buffer length supplied in pcchReaders, writes the length of the buffer that would have been returned if this parameter had not been NULL to pcchReaders, and returns a success code.

[in, out] pcchReaders

Length of the mszReaders buffer in characters. This parameter receives the actual length of the multi-string structure, including all trailing null characters. If the buffer length is specified as SCARD_AUTOALLOCATE, then mszReaders is converted to a pointer to a byte pointer, and receives the address of a block of memory containing the multi-string structure. This block of memory must be deallocated with SCardFreeMemory.

Return value

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

Return code/value	Description
Success 0 (0x0)	SCARD_S_SUCCESS
Group contains no readers 2148532270 (0x8010002E)	SCARD_E_NO_READERS_AVAILABLE
Specified reader is not currently available for use 2148532247 (0x80100017)	SCARD_E_READER_UNAVAILABLE
Other	An error code. For more information, see Smart Card Return Values.

Remarks

The SCardListReaders function is a database query function. For more information on other database query functions, see Smart Card Database Query Functions.

Examples

The following example shows listing the readers.

LPTSTR          pmszReaders = NULL;
LPTSTR          pReader;
LONG            lReturn, lReturn2;
DWORD           cch = SCARD_AUTOALLOCATE;

// Retrieve the list the readers.
// hSC was set by a previous call to SCardEstablishContext.
lReturn = SCardListReaders(hSC,
                           NULL,
                           (LPTSTR)&pmszReaders,
                           &cch );
switch( lReturn )
{
    case SCARD_E_NO_READERS_AVAILABLE:
        printf("Reader is not in groups.\n");
        // Take appropriate action.
        // ...
        break;

    case SCARD_S_SUCCESS:
        // Do something with the multi string of readers.
        // Output the values.
        // A double-null terminates the list of values.
        pReader = pmszReaders;
        while ( '\0' != *pReader )
        {
            // Display the value.
            printf("Reader: %S\n", pReader );
            // Advance to the next value.
            pReader = pReader + wcslen((wchar_t *)pReader) + 1;
        }
        // Free the memory.
        lReturn2 = SCardFreeMemory( hSC,
                                   pmszReaders );
        if ( SCARD_S_SUCCESS != lReturn2 )
            printf("Failed SCardFreeMemory\n");
        break;

default:
        printf("Failed SCardListReaders\n");
        // Take appropriate action.
        // ...
        break;
}

Note

The winscard.h header defines SCardListReaders 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.

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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