Errno vs. Stderr

Attribute	Errno	Stderr
Definition	System error number	Standard error stream
Usage	Used to identify errors in system calls	Used to output error messages
Value	Numeric value representing an error	Textual message describing an error
Location	Associated with system calls	Associated with output streams

Introduction

When it comes to error handling in programming, two commonly used concepts are Errno and Stderr. Both of these play a crucial role in providing information about errors that occur during program execution. In this article, we will compare the attributes of Errno and Stderr to understand their differences and similarities.

Errno

Errno, short for "error number," is a system variable in Unix-like operating systems that stores error codes for system calls. When a system call fails, it sets the value of Errno to a specific error code that indicates the type of error that occurred. Programmers can use Errno to identify and handle errors in their code effectively.

Errno values are typically defined in the header file, which contains a list of error codes and their corresponding meanings. By checking the value of Errno after a system call, programmers can determine the cause of the error and take appropriate action to handle it.

One important thing to note about Errno is that it is thread-specific, meaning that each thread in a multi-threaded program has its own Errno value. This can be both an advantage and a disadvantage, depending on the context in which Errno is being used.

Overall, Errno provides a standardized way to handle errors in Unix-like operating systems, making it a valuable tool for programmers working on these platforms.

Stderr

Stderr, short for "standard error," is a file descriptor in Unix-like operating systems that is used to output error messages. Unlike stdout, which is used for normal program output, stderr is specifically reserved for error messages that need to be displayed to the user or logged for debugging purposes.

When a program encounters an error, it can write error messages to stderr using functions like fprintf or fputs. These messages are typically displayed on the terminal where the program is running, making it easy for users to see what went wrong during program execution.

One advantage of using stderr for error messages is that it separates them from normal program output, making it easier to distinguish between the two. This can be especially useful in situations where a program generates a large amount of output, and it is important to highlight any errors that occur.

Another benefit of stderr is that it can be redirected to a file or another program using shell redirection operators, allowing for more flexibility in how error messages are handled and logged. This can be useful in scenarios where error messages need to be saved for later analysis or sent to a different system for monitoring.

Comparison

While Errno and Stderr serve different purposes in error handling, they both play important roles in ensuring that programs can effectively handle errors and provide meaningful feedback to users. Errno is more focused on providing error codes that can be used to identify the cause of an error, while stderr is used to display error messages to users.

• Errno is a system variable that stores error codes, while stderr is a file descriptor used for error output.
• Errno is thread-specific, while stderr is shared across all threads in a program.
• Errno provides standardized error codes, while stderr allows for customizable error messages.
• Errno is typically used for system calls, while stderr is used for general error reporting.

Overall, both Errno and Stderr are essential tools for programmers when it comes to handling errors in their programs. By understanding the differences and similarities between these two concepts, developers can effectively diagnose and resolve issues that arise during program execution.