Explore the full potential of C++ by mastering the standard library.

Become a C++ Programmer

The C++ standard library is a collection of all the tools and utilities available in C++. It received its latest update in 2017, known as C++17. The update introduces many new features that further optimize our code. This module will help us fully grasp C++ and use it to its full potential.

C++ Standard Library

Flags represent the state of the stream `stream`. The methods for dealing with these flags need the header `<iostream>`. Flags representing the state of a stream are:

| **Flag**  | **Query of the flag** | **Description**| 
|-|-|-|
|  `std::ios::goodbit` | `stream.good()` | No bit set | 
|  `std::ios::eofbit` | `stream.eof()` | end-of-file bit set | 
|  `std::ios::failbit` | `stream.fail()` | Error | 
|  `std::ios::badbit` | `stream.bad()` | Undefined behaviour | 
<p> <strong> State of a stream </strong> </p>

Here are examples of conditions causing the different states of a stream:

`std::ios::eofbit`:
* Reading beyond the last valid character.

`std::ios::failbit`:
* False formatted reading.
* Reading beyond the last valid character.
* Opening of a file went wrong. 

`std::ios::badbit`:
* Size of the stream buffer cannot be adjusted.
* Code conversion of the stream buffer went wrong.
* A part of the stream threw an exception. 

`stream.fail()`:
* returns whether `std::ios::failbit` or `std::ios::badbit` is set.

The state of a stream can be read and set. 

`stream.clear()`: 
\
Initializes the flags and sets the stream in the `goodbit` state.

`stream.clear(sta)`:
\
Initializes the flags and set the stream into `sta` state.

`stream.rdstate()`: 
\
Returns the current state.

`stream.setstate(fla)`: 
\
Sets the additional flag `fla`.

Operations on a stream only work if the stream is in the `goodbit` state. If the stream is in the `badbit` state you cannot set it to `goodbit` state.

Are there tools we can use in C++ which allow us to check the current condition of the stream? Flags answer this question.

State of the Stream