`fread`

Reads binary data from a file.

Category: Data Import and Analysis > Data Import and Export

Syntax

A = fread(fid)

Reads the rest of the file as unsigned bytes into a column of doubles.

A = fread(fid, sizeA, precision)

Reads sizeA values of the given type.

A = fread(fid, sizeA, precision, skip, machinefmt)

Skips bytes between values and sets the byte order.

[A, count] = fread(...)

Also returns the number of values read.

Description

Reading starts at the current file position and moves it forward, so successive calls walk through the file. Open the file in binary mode for non-text data. To read a text file as characters in one call, fread(fid, Inf, '*char')' returns the whole content.

Input arguments

sizeA: n for a column of up to n values, Inf for all, or [m n] to fill an m-by-n matrix column by column.
precision: Type in the file, such as 'uint8', 'int16', 'single', 'double', 'char'. Write 'uint8=>char' to also convert the output, or '*char' as a shorthand for the same type in and out.
machinefmt: Byte order: 'l' little-endian, 'b' big-endian.

Output arguments

A: Data read. The class is double unless the precision uses => or *.
count: Number of values read.

Example

Mixed binary record

fid = fopen('f.bin', 'w');
fwrite(fid, 'ABC');
fwrite(fid, pi, 'double');
fwrite(fid, [1 2], 'int16', 'b');
fclose(fid);
fid = fopen('f.bin');
txt = fread(fid, 3, '*char')'
x = fread(fid, 1, 'double')
v = fread(fid, 2, 'int16', 0, 'b')'
fclose(fid);

Output

txt = 'ABC'
x = 3.1416
v = 1×2

     1     2

fread