MATLAB Answers

check if a file exists

3,966 ビュー (過去 30 日間)
Salvatore Mazzarino
Salvatore Mazzarino 2012 年 9 月 29 日
コメント済み: sesilia maidelin 2021 年 7 月 22 日
I'm using the "importdata" function to import data from a text file. I would like to have a way to check if the text file exists before attempting to import data from the file. If the file doesn't exist, I would then like to display a custom error message. What is the function that I should use?

採用された回答

Jan
Jan 2012 年 9 月 29 日
編集済み: MathWorks Support Team 2018 年 11 月 9 日
Starting in R2017b, you can use the "isfile" function to check if a file exists. For example:
if isfile(filename)
% File exists.
else
% File does not exist.
end
The "isfile" function searches for files only on the specified path or in the current folder.
For R2017a and previous releases, use the "exist" function. For example:
if exist(filename, 'file') == 2
% File exists.
else
% File does not exist.
end
Be sure to specify an absolute path for the file name. The "exist" function searches all files and folders on the search path, which can lead to unexpected results if multiple files with the same name exist.
  5 件のコメント
sesilia maidelin
sesilia maidelin 2021 年 7 月 22 日
hi there, thanks for replying @Jan , in my case i just want to know the existence of a particular file type in a folder, then move the folder to another parentfolder named complete. so if the folder AAA contains a .txt and .jpgs, i want to move AAA into the folder complete that contains folder AAZ, BBA, etc that also contain .txt and .jpg files. i attached the picture of how the source file look like. I want to move files like 00000715 to the folder complete. Thank you!

サインインしてコメントする。

その他の回答 (5 件)

Image Analyst
Image Analyst 2012 年 9 月 29 日
if exist(fullFileName, 'file')
% File exists. Do stuff....
else
% File does not exist.
warningMessage = sprintf('Warning: file does not exist:\n%s', fullFileName);
uiwait(msgbox(warningMessage));
end
  3 件のコメント
Image Analyst
Image Analyst 2016 年 3 月 4 日
It checks if a file with that filename is there. It does not check what the contents are, or even if there are contents. It's possible to have a file with zero bytes. You can use fileInfo = dir(filename) to check size.

サインインしてコメントする。


Azzi Abdelmalek
Azzi Abdelmalek 2012 年 9 月 29 日
編集済み: Azzi Abdelmalek 2012 年 9 月 29 日
a=dir % or a=dir('folder')
b=struct2cell(a)
any(ismember(b(1,:),'filename.txt'))
  2 件のコメント
Jan
Jan 2019 年 5 月 6 日
But if the current directory contains a huge number of files, it is a waste of time. If the current folder is in a network drive, the slow down is substantial. This is more efficient:
isfile(fullfile(cd, 'filename.txt'))
And if it is unknown, if the file contains a path or not, use https://www.mathworks.com/matlabcentral/fileexchange/28249-getfullpath

サインインしてコメントする。


José-Luis
José-Luis 2012 年 9 月 29 日
編集済み: José-Luis 2012 年 9 月 29 日
doc exist

Simon
Simon 2016 年 11 月 2 日
編集済み: Simon 2016 年 11 月 2 日
A more modern / more succinct approach:
assert( exist( filename, 'file ) == 2, 'File not found.' );
Assert is a wonderful thing, and makes error-catching code a lot more compact than lots of if blocks! The way it works is,
assert( condition, error );
where condition is something that returns a logical true or false, and error is the message that results if it's false.
  2 件のコメント
Image Analyst
Image Analyst 2016 年 11 月 17 日
Though a friendlier more informative error message (like in my answer) would be an improvement.
But you're not totally correct. Like you said "exist(filename,'file') == 2 would occur when the file DOES exist." and exist(filename,'file') == 2 would be FALSE when the file DOES NOT exist. Since assert only spits out the error message when the file does not exist (the condition is false), it was correct as Simon originally had it, not your "correction".
Remember, in summary, if the file does exist, the condition is true, and the 'File not found.' message is not printed to the command window. If the file does NOT exist, the condition is false, and so the 'File not found.' message is printed to the command window.

サインインしてコメントする。


ABHAY K K
ABHAY K K 2019 年 2 月 4 日
is there a way to check the files exists in a particular directory without using the filename, What i mean to say is the more generalised way to find out
  2 件のコメント
Image Analyst
Image Analyst 2020 年 10 月 11 日
No. If you don't know the filename(s), you cannot determine if a file exists. The best you could do is to see if ANY files exist in the folder by using the dir() function.

サインインしてコメントする。

タグ

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by