difference between ios::ate and ios::trunc

[oontvoo]

Can anyone explain what the difference between using flag trunc and ate is?
It'd be nice if you could give some examples to show the difference.

By the way, what does "ate" stand for?

EDIT: I have replaced app with trunc, as what I really meant was what is the difference between trunc and ate?

[helios]

std::ios::app doesn't truncate the file when it is opened, and std::ios::ate puts the file pointer at the end of the file. This is useful to get the file size:

std::ifstream file("file.txt",std::ios::binary|std::ios::ate);
unsigned long size=file.tellg();

Without std::ios::ate, you'd have to call file.seekg(0,std::ios::end) before line 2.

[oontvoo]

Well, I think I made a mistake. What I meant was

What is the difference between trunc and ate

But thanks anyways for the explanation!

[helios]

Oops. I completely misread that.

std::ios::trunc ensures that the file will be truncated.