How to Read File in MATLAB: Syntax and Examples

In MATLAB, you can read files using functions like fopen to open the file, fread or fscanf to read data, and fclose to close the file. For structured data like tables, use readtable for easy reading of CSV or text files.

Syntax

Here are common ways to read files in MATLAB:

• fid = fopen(filename, permission): Opens a file and returns a file ID.
• data = fread(fid, size, precision): Reads binary data from the file.
• data = fscanf(fid, formatSpec): Reads formatted data as text.
• fclose(fid): Closes the opened file.
• tableData = readtable(filename): Reads tabular data from a file into a table.

matlab

fid = fopen('data.txt', 'r');
data = fscanf(fid, '%f');
fclose(fid);

tableData = readtable('data.csv');

Example

This example reads numbers from a text file named numbers.txt and prints them. It also shows how to read a CSV file into a table.

matlab

fid = fopen('numbers.txt', 'r');
if fid == -1
    error('File cannot be opened');
end
numbers = fscanf(fid, '%f');
fclose(fid);
disp('Numbers read from file:');
disp(numbers);

% Reading CSV file into a table
filename = 'data.csv';
tableData = readtable(filename);
disp('Table data:');
disp(tableData);

Output

Numbers read from file:
     1
     2
     3
     4
     5
Table data:
    Name      Age    Score
    _____    ____    _____
    'Amy'     25      88
    'Bob'     30      92
    'Cara'    22      95

Common Pitfalls

Common mistakes when reading files in MATLAB include:

• Not checking if fopen successfully opened the file (it returns -1 if it fails).
• Forgetting to close the file with fclose, which can lock the file.
• Using wrong format specifiers in fscanf causing incorrect data reading.
• Trying to read structured data with fscanf instead of readtable for CSV or tabular files.

matlab

%% Wrong way: Not checking fopen result
fid = fopen('missing.txt', 'r');
if fid == -1
    error('File not found or cannot be opened');
end
% Proceed to read
fclose(fid);

%% Right way: Check fopen
fid = fopen('missing.txt', 'r');
if fid == -1
    error('File not found or cannot be opened');
end
% Proceed to read
fclose(fid);

Quick Reference

Summary tips for reading files in MATLAB:

• Use fopen, fread, fscanf, and fclose for low-level file reading.
• Use readtable for CSV or structured text files.
• Always check if the file opened successfully.
• Close files after reading to free resources.

Key Takeaways

Use fopen and fclose to open and close files safely in MATLAB.

Use fscanf or fread to read raw data, and readtable for structured tables.

Always check if fopen returns a valid file ID before reading.

Close files after reading to avoid locking issues.

Choose the right reading function based on file type and data format.