# <system_error>

**[<system_error>](https://en.cppreference.com/w/cpp/header/system_error)** provides `std::error_code` and `std::error_category` for OS-level error reporting. Use it to portably capture and classify system errors (like `errno` or Windows HRESULT) without hardcoding values.

Most code doesn't use this directly; it's used internally by file operations and network APIs.

## Example

This example captures an error when opening a nonexistent file and describes it using the generic error category.

```cpp
// compile: g++ -std=c++11 -o systemerrorexample systemerrorexample.cpp
// run: ./systemerrorexample
// description: system error handling

#include <system_error>
#include <fstream>
#include <iostream>

int main() {
    std::ifstream file("nonexistent.txt");
    if (!file) {
        std::error_code ec(errno, std::generic_category());
        std::cout << "error: " << ec.message() << "\n";
    }
    
    return 0;
}
```