fwrite

Write data in binary form to the file specified by the file descriptor fid.

📝 Syntax

• count = fwrite(fid, data)

• count = fwrite(fid, data, precision)

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

• count = fwrite(fid, data, precision, skip, arch)

• count = fwrite(fid, data, precision, arch)

• [count, bytes] = fwrite(fid, ...)

📥 Input argument

• fid - a file descriptor

• data - data to write

• precision - class of values to read

• skip - number of bytes to skip

• arch - a string specifying the data format for the file.

📤 Output argument

• count - -1 or number of elements written

• bytes - number of bytes written

📄 Description

Write data in binary form to the file specified by the file descriptor fid.

characters encoding uses fopen parameter.

supported architecture:

native , n: format of the current machine.

ieee-be, b: IEEE big endian.

ieee-le, l: IEEE little endian.

supported precision:

Value Type	Precision	Bits (Bytes)
Logical	'logical'	platform-dependent
Floating-point numbers	'double', 'real*8', 'float64'	64 (8)
'single', 'real*4', 'float32'	32 (4)
Integers, signed	'int'	32 (4)
'int8', 'integer*1', 'schar'	8 (1)
'int16', 'integer*2'	16 (2)
'int32', 'integer*4'	32 (4)
'int64', 'integer*8'	64 (8)
Integers, unsigned	'uint8', 'uchar'	8 (1)
'uint16'	16 (2)
'uint32'	32 (4)
'uint64'	64 (8)
Characters	'char', '*char'	depends encoding with fopen.
'char*1'	depends encoding with fopen.

if fwrite fails, it returns a negative value.

iffwrite succeeds, it returns the number of elements written successfully.

iffwrite writes characters, it returns the number of characters written successfully and not the number of elements.

💡 Examples

A = rand(3,1)

fileID = fopen([tempdir(), 'doubledata.bin'],'w');
fwrite(fileID, A,'double');
fclose(fileID);

fileID = fopen([tempdir(), 'doubledata.bin'],'r');
R = fread(fileID, 'double')
fclose(fileID);

test_string =  'é ö ä ü è ê';
fid = fopen([tempdir(), 'fwrite_example_char.txt'], 'w','n', 'UTF-8');
[count, bytes] = fwrite(fid, test_string) % returns 11 and 17
fclose(fid);

% This is the number of characters written and not the number of bytes.
% Each accented character (é, ö, ä, ü, è, ê) = 2 bytes each
% Each space = 1 byte
% Total bytes = 6*2 + 5*1 = 17 bytes

🔗 See also

fopen, fclose, fread.

🕔 History

Version	📄 Description
1.0.0	initial version
1.15.0	fwrite returns the number of characters written for character data.