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I am new to C++. I have simple question to ask you that what is the difference between std::fstream::X and std::ios::X open file mode in C++ ?

Where x can be in, out, ate, trunk, ate ?

Here is more example:

fs.open(filename.c_str(), std::fstream::in | std::fstream::out | std::fstream::app);

vs

fs.open(filename.c_str(), std::ios::in | std::ios::out | std::ios::app);

what is the difference between these two ?

Please don't answer in a complicated manner since I am beginner in C++.

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  • It's inheritance working there Commented Jan 11, 2016 at 13:55
  • what does mean this ? Commented Jan 11, 2016 at 13:56
  • ios is base class of fstream Commented Jan 11, 2016 at 13:57
  • so what do it ? can so explain in more detail please.. with an possible example Commented Jan 11, 2016 at 13:58

3 Answers 3

Reset to default
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Quoting Input/Output in File

class: default mode parameter

ofstream: ios::out

ifstream: ios::in

fstream: ios::in | ios::out

For ifstream and ofstream classes, ios::in and ios::out are automatically and respectively assumed, even if a mode that does not include them is passed as second argument to the open() member function.

std::fstream is inherited from std::ios, according to this page

When reading from a file, I prefer to use std::ifstream::in flag, because it could be a good programming practice to let a programming interface know what you are going to use it for.

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2 Comments

what means inherited ?
@Aryan It means the inheritance in C++, one good resource is here
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There's no difference. std::fstream::X is inherited from std::ios, so it's the same value as std::ios::X.

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1

Alice has a son, Bob. They both have the same hair color -- brown, let's say. Now, someone asks you: "What's their family's hair color?" You could say Alice's or Bob's: it's the same.

Can you see the point? Although the color is the same, Bob has inherited her mother's. It's the same for std::ios::in and std::fstream::in -- it's the same value, since they have an inheritance relation, but it's their "own" value because they are not the same type (likewise, Alice and Bob are not the same person).

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