# <ios>

**[<ios>](https://en.cppreference.com/w/cpp/header/ios)** defines the base classes for input/output streams: `std::ios_base`, `std::basic_ios`. It handles stream state (good, fail, eof), format flags, and locale.

Most user code works with derived classes like `std::cin`, `std::cout`, `std::fstream`, and doesn't interact with this header directly.

## Example

This example sets format flags on cout to display output in hexadecimal and fixed-point notation.

```cpp
// compile: g++ -std=c++11 -o iosexample iosexample.cpp
// run: ./iosexample
// description: check stream state and set format flags

#include <ios>
#include <iostream>

int main() {
    std::cout.setf(std::ios::hex, std::ios::basefield);
    std::cout << 42 << "\n";
    
    std::cout.setf(std::ios::fixed | std::ios::showpoint);
    std::cout << 3.14 << "\n";
    
    return 0;
}
```