SCardListReadersA function (winscard.h)
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).
[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 |
---|---|
|
SCARD_S_SUCCESS |
|
SCARD_E_NO_READERS_AVAILABLE |
|
SCARD_E_READER_UNAVAILABLE |
|
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 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 |