CODEWITHSUNDEEP
c++std
datguyray
datguyray

Reputation: 141

How to determine if std::filesystem::remove_all failed?

I am trying to use the non-throwing version of std::filesystem::remove_all, I have something like:

bool foo()
{
  std::error_code ec;
  std::filesystem::remove_all(myfolder, ec);

  if (ec.value())
  {
    // failed to remove, return
    return false;
  }
}

Is this the correct way to use error_code?

My reasoning:

I read this:

The overload taking a std::error_code& parameter sets it to the OS API error code if an OS API call fails, and executes ec.clear()

Now here:

clear - sets the error_code to value 0 in system_category

Now I used this to imply error_code == 0 => No error. error_code != 0 => error.

I really can't any much examples of uses of error_code. I just want to determine if all the files have been removed or not.

Upvotes: 1

Views: 1040

Answers (1)

Yakk - Adam Nevraumont
Yakk - Adam Nevraumont

Reputation: 275500

There is a difference between ec.value() and ec != std::error_code{}; in the case where the error code in ec is a different error category than system error and has a value of 0, the first will return false, while the second will return true.

Error codes are a tuple of categories and value. Looking only at the value is a tiny bit of "code smell".

In this case, I don't think it is possible for the error code to have anything except the system category. And it would be bad form for a non-system error category to use the value 0 for an actual error.

If there was no error (value 0) with a non-system error code, treating it like an error is probably a bad idea. So maybe you shouldn't be checking the category.

Finally, if (ec.value()) is a verbose way of saying if (ec). I'd use the explicit operator bool() const instead of calling .value().

Another option is:

if (-1 == std::filesystem::remove_all(myfolder, ec)) {
  // failed to remove, return
  return false;
}

Upvotes: 2

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