writing function..

fwrite


Write binary data to a file

Syntax

• count = fwrite(fid,A,precision)
  count = fwrite(fid,A,precision,skip)
  

Description

count = fwrite(fid,A,precision) writes the elements of matrix A to the specified file, translating MATLAB values to the specified precision. The data is written to the file in column order, and a count is kept of the number of elements written successfully.

fid is an integer file identifier obtained from fopen, or 1 for standard output or 2 for standard error.

precision controls the form and size of the result. For 'bitN' or 'ubitN' precisions, fwrite sets all bits in A when the value is out-of-range.

count = fwrite(fid,A,precision,skip) includes an optional skip argument that specifies the number of bytes to skip before each precision value is written. With the skip argument present, fwrite skips and writes one value, skips and writes another value, etc. until all of A is written. If precision is a bit format like 'bitN' or 'ubitN', skip is specified in bits. This is useful for inserting data into noncontiguous fields in fixed-length records.

Examples

For example,

• fid = fopen('magic5.bin','wb');
  fwrite(fid,magic(5),'integer*4')
  

creates a 100-byte binary file, containing the 25 elements of the 5-by-5 magic square, stored as 4-byte integers.

fwrite (serial)

Write binary data to the device

Syntax

• fwrite(obj,A)
  fwrite(obj,A,'precision')
  fwrite(obj,A,'mode')
  fwrite(obj,A,'precision','mode')
  

Arguments

obj	A serial port object.
A	The binary data written to the device.
'precision'	The number of bits written for each value, and the interpretation of the bits as character, integer, or floating-point values.
'mode'	Specifies whether data is written synchronously or asynchronously.

Description

fwrite(obj,A) writes the binary data A to the device connected to obj.

fwrite(obj,A,'precision') writes binary data with precision specified by precision.

precision controls the number of bits written for each value and the interpretation of those bits as integer, floating-point, or character values. If precision is not specified, uchar (an 8-bit unsigned character) is used.

fwrite(obj,A,'mode') writes binary data with command line access specified by mode. If mode is sync, A is written synchronously and the command line is blocked. If mode is async, A is written asynchronously and the command line is not blocked. If mode is not specified, the write operation is synchronous.

fwrite(obj,A,'precision','mode') writes binary data with precision specified by precision and command line access specified by mode.

Remarks

Before you can write data to the device, it must be connected to obj with the fopen function. A connected serial port object has a Status property value of open. An error is returned if you attempt to perform a write operation while obj is not connected to the device.

The ValuesSent property value is increased by the number of values written each time fwrite is issued.

An error occurs if the output buffer cannot hold all the data to be written. You can specify the size of the output buffer with the OutputBufferSize property.

If you use the help command to display help for fwrite, then you need to supply the pathname shown below.

• help serial/fwrite
  

Synchronous Versus Asynchronous Write Operations

By default, data is written to the device synchronously and the command line is blocked until the operation completes. You can perform an asynchronous write by configuring the mode input argument to be async. For asynchronous writes:

• The BytesToOutput property value is continuously updated to reflect the number of bytes in the output buffer.
• The M-file callback function specified for the OutputEmptyFcn property is executed when the output buffer is empty.

You can determine whether an asynchronous write operation is in progress with the TransferStatus property.

Synchronous and asynchronous write operations are discussed in more detail in Writing Data.

Rules for Completing a Write Operation with fwrite

A binary write operation using fwrite completes when:

• The specified data is written.
• The time specified by the Timeout property passes.

Note The Terminator property is not used with binary write operations.

Supported Precisions

The supported values for precision are listed below.

Data Type	Precision	Interpretation
Character	uchar	8-bit unsigned character
	schar	8-bit signed character
	char	8-bit signed or unsigned character
Integer	int8	8-bit integer
	int16	16-bit integer
	int32	32-bit integer
	uint8	8-bit unsigned integer
	uint16	16-bit unsigned integer
	uint32	32-bit unsigned integer
	short	16-bit integer
	int	32-bit integer
	long	32- or 64-bit integer
	ushort	16-bit unsigned integer
	uint	32-bit unsigned integer
	ulong	32- or 64-bit unsigned integer
Floating-point	single	32-bit floating point
	float32	32-bit floating point
	float	32-bit floating point
	double	64-bit floating point
	float64	64-bit floating point