IByteBuffer::Read method

Стаття
01/07/2021

[The Read method is available for use in the operating systems specified in the Requirements section. It is not available for use in Windows Server 2003 with Service Pack 1 (SP1) and later, Windows Vista, Windows Server 2008, and subsequent versions of the operating system. The IStream interface provides similar functionality.]

The Read method reads a specified number of bytes from the buffer object into memory starting at the current seek pointer.

Syntax

HRESULT Read(
  [out] BYTE *pByte,
  [in]  LONG cb,
  [out] LONG *pcbRead
);

Parameters

pByte [out]: Points to the buffer into which the stream data is read. If an error occurs, this value is NULL.
cb [in]: Number of bytes of data to attempt to read from the stream object.
pcbRead [out]: Address of a LONG variable that receives the actual number of bytes read from the stream object. You can set this pointer to NULL to indicate that you are not interested in this value. In this case, this method does not provide the actual number of bytes read.

Return value

The return value is an HRESULT. A value of S_OK indicates the call was successful.

Remarks

This method reads bytes from this stream object into memory. The stream object must be opened in STGM_READ mode. This method adjusts the seek pointer by the actual number of bytes read.

The number of bytes actually read is also returned in the pcbRead parameter.

Notes to Callers

The actual number of bytes read can be fewer than the number of bytes requested if an error occurs or if the end of the stream is reached during the read operation.

Some implementations might return an error if the end of the stream is reached during the read. You must be prepared to deal with the error return or S_OK return values on end of stream reads.

Examples

The following example shows reading bytes from the buffer.

BYTE     byAtr[32];
long     lBytesRead, i;
HRESULT  hr;

// pAtr is a pointer to a previously instantiated IByteBuffer.
// It was used in an earlier call by ISCard::get_Atr.
// Use IByteBuffer::Read to access the retrieved ATR bytes.
hr = pAtr->Read(byAtr, 32, &lBytesRead);
// Use the ATR value. (This example merely displays the bytes.)
for ( i = 0; i < lBytesRead; i++)
    printf("%c", *(byAtr + i));
printf("\n");

Requirements

Requirement	Value
Minimum supported client	Windows XP [desktop apps only]
Minimum supported server	Windows Server 2003 [desktop apps only]
End of client support	Windows XP
End of server support	Windows Server 2003
Header	Scardssp.h
Type library	Scardssp.tlb
DLL	Scardssp.dll
IID	IID_IByteBuffer is defined as E126F8FE-A7AF-11D0-B88A-00C04FD424B9

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