12.3.108 user_write()


  void *user_data,
  void const *buf,
  size_t *pbuf_size,
  spio_t_bits write_options

This is the prototype for one of the methods of user defined streams. It is used when SICStus wants to write data to the user defined stream.



The same value as was passed to SP_create_stream().


Points to a buffer allocated by the caller containing the data to be written.


Points to the size of the buffer, always positive. When this function returns successfully, *pbuf_size should be set to the number of bytes actually written, which should always be positive for successful return.

Note that buffer size is measured in bytes also for text streams.


The following bits can be set:


This is always specified if the device was created as a binary device. The buffer contains *pbuf_size bytes.


This is always specified if the device was created as a text device. The buffer contains wide characters, i.e. spio_t_wchar. Note that *buf_size is size in bytes, not in characters.


If this is set, the function should return quickly, either with some data written or with a SPIO_E_WOULD_BLOCK code.

If your user_write will never block, you can ignore this value.

You should return SPIO_E_NOT_SUPPORTED if user_write cannot support non-blocking write.

Return Value

On success, *pbuf_size should be assigned to with the number of bytes written and SPIO_S_NOERR or some other success code returned. On success, something must have been written, e.g. *pbuf_size must be set to a positive value.

On failure, return a SPIO error code. Error codes with special meaning for user_write:


Returned if it is not possible to write more data onto the stream, e.g. some underlying device has been closed.


SPIO_DEVICE_WRITE_OPTION_NONBLOCKING was set but the operation would block.


Some unsupported option, e.g. SPIO_DEVICE_WRITE_OPTION_NONBLOCKING, was passed.

Other error codes may also be returned.


Should write up to *buf_size bytes of data from buf. Data could be either bytes, for a binary device, or wide characters, for a text device.

See Also

cpg-ref-SP_create_stream. Defining a New Stream.

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