---
title: "2.13 std::cerr"
description: "The `std::cerr` object is the standard error output stream in C++. It is used to display error messages and diagnostic information separately from normal program output. Keeping error messages on a separate stream allows them to be redirected or processed…"
url: "https://edcret.in/docs/cpp-programming/input-and-output-cplusplus/2-13-stdcerr/"
updated: "2026-07-28"
category: C++ Programming / Input and Output
---

# 2.13 std::cerr

The `std::cerr` object is the standard error output stream in C++. It is used to display error messages and diagnostic information separately from normal program output. Keeping error messages on a separate stream allows them to be redirected or processed independently.

Unlike `std::cout`, the `std::cerr` stream is unbuffered. This means that error messages are written to the output device immediately without waiting for the output buffer to fill.

## Source Code

```
#include <iostream>

int main()
{
    std::cout << "Program started.\n";

    std::cerr << "Error: Unable to open the file.\n";

    std::cout << "Program terminated.\n";

    return 0;
}
```

## Output

```
Program started.
Error: Unable to open the file.
Program terminated.
```

## Explanation

- `std::cerr` is the standard error output stream defined in the `<iostream>` library.
- It is primarily used to display error messages, warnings, and diagnostic information.
- Unlike `std::cout`, `std::cerr` is unbuffered, so its output is displayed immediately.
- Separating normal output (`std::cout`) from error output (`std::cerr`) makes it easier to redirect or log each stream independently.
- The stream insertion operator (`<<`) is used with `std::cerr` in the same way as with `std::cout`.
- Using `std::cerr` helps distinguish program errors from regular program output.
- `return 0;` terminates the program successfully.