fopen always open the file even when it is already open

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Florian Bidaud
Florian Bidaud 2022-10-19
评论： Florian Bidaud 2022-10-19
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 !

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采纳的回答

Jan
Jan 2022-10-19
编辑：Jan 2022-10-19
"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.
  1 个评论
Florian Bidaud
Florian Bidaud 2022-10-19
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.

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