what is the best way to check a file's existence and file permissions in linux using c++

Question

I am using boost::filesystem::exists() to check file's existence.

Is there a better way to do it?

Also how do I find file permissions ?

Answer 1

The only correct way to check if a file exists is to try to open it. The only correct way to check if a file is writable is to try to open it for writing. Anything else is a race condition. (Other API calls can tell you if the file existed a moment ago, but even if it did, it might not exist those 15 nanoseconds later, when you try to actually open it, so they're largely useless)

However, if you want to know if a file exists without opening it, simply use the boost::filesystem::exists function. But be aware of the gaping flaw in it. It doesn't tell you if the file exists, it tells you if the file existed.

So be careful how you use it. Don't assume that just because the function returned true, that the file will exist when you actually try to open it.

If you need to know "will I be able to open this file", then the only way to find out is to try to open it.