Reading text files (readtable, textscan) in MATLAB - Step-by-Step Execution

Concept Flow - Reading text files (readtable, textscan)

Open file with fopen

↓

Choose method: readtable or textscan

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readtable reads entire table

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Store data in table

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Close file with fclose

This flow shows how MATLAB opens a file, reads data using readtable or textscan, stores it, and then closes the file.

Execution Sample

MATLAB

fid = fopen('data.txt');
data = textscan(fid, '%s %d %f');
fclose(fid);

This code opens a text file, reads three columns (string, integer, float) using textscan, then closes the file.

Execution Table

Step	Action	Input/Format	Result	Notes
1	fopen	'data.txt'	File ID (fid) assigned	File opened for reading
2	textscan	'%s %d %f'	Cell array with 3 columns	Reads string, int, float columns
3	fclose	fid	File closed	Releases file resource
4	End	-	-	File reading complete

💡 File closed after reading all data with textscan

Variable Tracker

Variable	Start	After fopen	After textscan	After fclose
fid	undefined	file ID (e.g. 3)	file ID (unchanged)	closed (no longer valid)
data	undefined	undefined	cell array with data	cell array with data (unchanged)

Key Moments - 3 Insights

Why do we need to use fclose after fopen?

fclose releases the file resource so other programs or MATLAB can access the file later. See execution_table step 3.

What does '%s %d %f' mean in textscan?

It tells textscan to read a string (%s), then an integer (%d), then a floating-point number (%f) from each line. See execution_table step 2.

Why choose readtable over textscan?

readtable automatically reads the whole file into a table with column names, easier for structured data. textscan is more flexible for custom formats.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'fid' after step 1?

A A file ID number (e.g., 3)

B Undefined

C Cell array with data

D Closed file

💡 Hint

Check execution_table row 1 under Result column

At which step is the file closed according to the execution_table?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look for 'fclose' action in execution_table

If the format string in textscan changes to '%f %f %f', what changes in the variable 'data'?

A data will be empty

B data will contain three columns of floating-point numbers

C data will contain strings only

D data will contain integers only

💡 Hint

Refer to key_moments about format specifiers and execution_table step 2

Concept Snapshot

Open file with fopen to get file ID
Use readtable for automatic table import
Or use textscan with format specifiers for custom reading
Close file with fclose to free resource
Data stored as table or cell arrays

Full Transcript

This visual execution shows how MATLAB reads text files using fopen, readtable, and textscan. First, fopen opens the file and returns a file ID. Then, readtable or textscan reads the data. readtable reads the whole file into a table automatically, while textscan reads data according to a format string like '%s %d %f'. After reading, fclose closes the file to release it. Variables like fid and data change during these steps. Key points include why fclose is needed, what format specifiers mean, and when to use readtable versus textscan.