ftell

Current location of file position pointer in file

Syntax

position = ftell(fileID)

Description

position = ftell(fileID) returns the current location of the position pointer in the specified file.

• If the query is successful, then position is a zero-based integer that indicates the number of bytes from the beginning of the file.

• If the query is unsuccessful, then position is -1.

Examples

Find Current Position in File

When you open a file, MATLAB® creates a pointer to indicate the current position within the file. Open the following badpoem.txt file and perform a read operation (which advances the position pointer). Then, query the final position in the file after the read operation.

Use fopen to open the file. Then, use ftell to query the current position.

fid = fopen('badpoem.txt');
ftell(fid)

ans = 
0

Using fgetl, read the first line and examine the current position after the read operation.

tline1 = fgetl(fid)  % read the first line 

tline1 = 
'Oranges and lemons,'

ftell(fid)

ans = 
20

Read the second line and examine the current position.

tline2 = fgetl(fid)  % read the second line 

tline2 = 
'Pineapples and tea.'

ftell(fid)

ans = 
40

Close the file.

fclose(fid);

Input Arguments

fileID — File identifier

integer

File identifier of an open file, specified as an integer. To open a file and obtain its identifier, use the fopen function.

Data Types: double

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

When the MATLAB^® behavior differs from the C compiler behavior, the generated code usually matches the C compiler behavior. For example, if you use fseek to seek past the end of a file, the behavior of ftell in the generated code matches the C compiler behavior.

Thread-Based Environment

Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool.

This function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

Version History

Introduced before R2006a

R2024b: Read data over HTTP and HTTPS using low-level file functions

You can read data from primary online sources by performing low-level file read operations over an internet URL.

R2022b: Use function in thread-based environments

This function supports thread-based environments.