C standard streams: what is stderr? Choose the most accurate description used in ISO C.

Introduction / Context:
C defines three standard text streams: stdin, stdout, and stderr. Understanding their roles is essential for proper error reporting and redirection.

Given Data / Assumptions:

• We are referring to the identifier stderr from <stdio.h>.
• It is implemented as a FILE* object.

Concept / Approach:

stderr is the standard error stream used for diagnostics and error messages. Unlike stdout, it is often unbuffered or line-buffered to ensure messages appear promptly, even if the program crashes or stdout is redirected.

Step-by-Step Solution:

Verification / Alternative check:

Run a program redirecting only stdout to a file; messages sent to stderr still appear in the terminal, illustrating the separate channel for errors.

Why Other Options Are Wrong:

standard error types: Not a defined term in C.

standard error streams: Plural is misleading; stderr is one stream.

standard error definitions: Not the concept being asked.

Common Pitfalls:

• Confusing buffering behavior of stderr vs stdout.
• Assuming errors must go to stdout.

Final Answer:

standard error