12.3.106 user_read()


       void *user_data,
       void *buf,
       size_t *pbuf_size,
       spio_t_bits read_options

This is the prototype for one of the methods of user defined streams. It is used when SICStus need to obtain more data from the user defined stream.


The same value as was passed to SP_create_stream().
Points to a buffer allocated by the caller.
Points to the size of the buffer. The buffer is always large enough to hold at least one byte (for binary streams) or one character (for text streams). When this function returns successfully, *pbuf_size should be set to the number of bytes stored in the buffer, 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 should be filled with up to *pbuf_size bytes.
This is always specified if the device was created as a text device. The buffer should be filled with wide characters, i.e. spio_t_wchar. Note that *buf_size is size in bytes, not in characters.
If this is set then the function should return quickly, either with some data read or with a SPIO_E_WOULD_BLOCK code.

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

You should return SPIO_E_NOT_SUPPORTED if user_read cannot support non-blocking read.

Return Value

On success, *pbuf_size should be assigned and SPIO_S_NOERR or some other success code returned.

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

Return this when there are no more data to read.
SPIO_DEVICE_READ_OPTION_NONBLOCKING was set but the operation would block.
Some unsupported option, e.g. SPIO_DEVICE_READ_OPTION_NONBLOCKING, was passed.

Other error codes may also be returned.


Should fill buf with up to *buf_size bytes of data. Data should be either bytes, for a binary device, or spio_t_wchar (32 bit) wide characters, for a text device.

See Also

cpg-ref-SP_create_stream. Defining a New Stream.

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