fopen always open the file even when it is already open

Hi,

fopen is supposed to return -1 when it can't open the file. So I thought when I had the file open already it would return -1. But when I do it I always have the same output. Have I misunderstood how fopen works ?

I also can't open the file anymore as it gets corrupted if I use 'w' or 'W' option for fopen. I haven't found any explanation to that behaviour.

>> fopen('myFile.xlsx')

ans =

     3

>> fclose('all')

ans =

     0
% Here I open the file in Excel
     
>> fopen(myFile)

ans =

     3

>> fclose('myFile.xlsx')

ans =

     0
     

Thank you !

Answer 1

[Jan]

"fopen is supposed to return -1 when it can't open the file" - correct, this is the defined behavior.

"So I thought when I had the file open already it would return -1." - no, this is not the case. See above: If Matlab can open the file, a file handle is replied. You can open a file multiple times for reading.

"Have I misunderstood how fopen works ?" - Yes.

"I also can't open the file anymore as it gets corrupted if I use 'w' or 'W' option for fopen." - correct. 'W' and 'w' open the file for writing. This crops the existing contents of the file. You find this documented in:

doc fopen

The posted code shows the expected behavior.

[Florian Bidaud]

Thank you for this answer.

I've read that page already.

I understand that we can open several files for reading, but I've found plenty of topics suggesting using fopen to check if an Excel file was already open, that's why I' m confused.