How to make c++ not create a new file if one doesn't exist?

Question

I've been working with c++ and I noticed that whenever I use .open() for a file if there's no file with that name, it just creates one. Is there a way to have it not do this?

Does this answer your question? Fastest way to check if a file exists using standard C++/C++11,14,17/C? — Christian
– Christian, Commented Apr 8, 2022 at 0:22
I find this chart form the C++ Standard helpful. I can then map it to this table to see what'll happen. If we open a file for "r+" which is an ofsteam opened with ios::in, the file will not open and will not be created. — user4581301
– user4581301, Commented Apr 8, 2022 at 1:00

user18741504 · Accepted Answer · 2022-04-08 00:18:02Z

2

Check if the file exists first. The following link might help you:

Fastest way to check if a file exists using standard C++/C++11,14,17/C?

Or maybe, you could use the nocreate option:

void open(const char *filename, ios::openmode mode); where,

First argument *filename specifies the name of file and location.
Second argument open() member function defines the mode in which the file should be opened.

All the options here: https://www.tutorialride.com/cpp/file-handling-in-c.htm

answered Apr 8, 2022 at 0:18

user18741504

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2 Comments

François Andrieux Over a year ago

Checking if the file already exists before trying to open it is not reliable, the file might have been deleted or moved between the moment you check and when you try to open it.

user4581301 Over a year ago

I recommend expanding on this answer to demonstrate which open modes will not create a new file. I've linked a few helpful tables above in the comments you can feel free to reference.

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