WinUsb_ReadPipe function (winusb.h)

The WinUsb_ReadPipe function reads data from the specified pipe.


BOOL WinUsb_ReadPipe(
  [in]            WINUSB_INTERFACE_HANDLE InterfaceHandle,
  [in]            UCHAR                   PipeID,
  [out]           PUCHAR                  Buffer,
  [in]            ULONG                   BufferLength,
  [out, optional] PULONG                  LengthTransferred,
  [in, optional]  LPOVERLAPPED            Overlapped


[in] InterfaceHandle

An opaque handle to the interface that contains the endpoint with which the pipe is associated.

To read data from the pipe associated with an endpoint in the first interface, use the handle returned by WinUsb_Initialize. For all other interfaces, use the handle to the target interface, retrieved by WinUsb_GetAssociatedInterface.

[in] PipeID

PipeID corresponds to the bEndpointAddress field in the endpoint descriptor. For information about the layout of this field, see Table 9-13 in "Universal Serial Bus Specification Revision 2.0" at USB Technology. In the bEndpointAddress field, Bit 7 indicates the direction of the endpoint: 0 for OUT; 1 for IN.

[out] Buffer

A caller-allocated buffer that receives the data that is read.

[in] BufferLength

The maximum number of bytes to read. This number must be less than or equal to the size, in bytes, of Buffer.

[out, optional] LengthTransferred

A pointer to a ULONG variable that receives the actual number of bytes that were copied into Buffer. For more information, see Remarks.

[in, optional] Overlapped

An optional pointer to an OVERLAPPED structure that is used for asynchronous operations. If this parameter is specified, WinUsb_ReadPipe returns immediately rather than waiting synchronously for the operation to complete before returning. An event is signaled when the operation is complete.

Return value

WinUsb_ReadPipe returns TRUE if the operation succeeds. Otherwise, this function returns FALSE, and the caller can retrieve the logged error by calling GetLastError.

GetLastError can return the following error code.

Return code Description
The caller passed NULL in the InterfaceHandle parameter.
An overlapped I/O operation is in progress but has not completed. If the overlapped operation cannot be completed immediately, the function returns FALSE and the GetLastError function returns ERROR_IO_PENDING, indicating that the operation is executing in the background. Call WinUsb_GetOverlappedResult to check the success or failure of the operation.
There is insufficient memory to perform the operation.
The read operation initiated by WinUsb_ReadPipe in the USB stack timed out before the operation could be completed.


If the data returned by the device is greater than a maximum transfer length, WinUSB divides the request into smaller requests of maximum transfer length and submits them serially. If the transfer length is not a multiple of the endpoint's maximum packet size (retrievable through the WINUSB_PIPE_INFORMATION structure's MaximumPacketSize member), WinUSB increases the size of the transfer to the next multiple of MaximumPacketSize.

USB packet size does not factor into the transfer for a read request. If the device responds with a packet that is too large for the client buffer, the behavior of the read request corresponds to the type of policy set on the pipe. If policy type for the pipe is ALLOW_PARTIAL_READS, WinUSB adds the remaining data to the beginning of the next transfer. If ALLOW_PARTIAL_READS is not set, the read request fails. For more information about policy types, see WinUSB Functions for Pipe Policy Modification.

If an application passes NULL in the Overlapped parameter (synchronous operation), the application must make sure that LengthTransferred is not NULL, even when the read operation produces no output data.

If Overlapped is not NULL (asynchronous operation), LengthTransferred can be set to NULL. For an overlapped operation (and if LengthTransferred is a non-NULL value), the value received in LengthTransferred after WinUsb_ReadPipe returns is meaningless until the overlapped operation has completed. To retrieve the actual number of bytes read from the pipe, call WinUsb_GetOverlappedResult.

When no data is available in the endpoint (pipe is empty), WinUsb_ReadPipe does not return until there is data in the pipe. If an error condition occurs or the application-specified timeout expires, WinUsb_ReadPipe always returns FALSE. To determine the actual reason for that return value, always call GetLastError. For example, in these cases the GetLastError error value indicates the actual reason:

  • If the application specified a timeout value in the pipe policy and that timeout expires, WinUsb_ReadPipe returns FALSE and GetLastError returns ERROR_SEM_TIMEOUT.
  • If an error condition occurs while reading data from the pipe, WinUsb_ReadPipe returns FALSE and GetLastError returns ERROR_GEN_FAILURE.


Target Platform Universal
Header winusb.h (include Winusb.h)
Library Winusb.lib
DLL Winusb.dll

See also


WinUSB Functions