Meaning of mode string in fopen: In the call fp = fopen("source.txt", "rb"); what does the mode "rb" instruct the C library to do?
C Programming
Input / Output
Difficulty: Easy
Choose an option
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Aopen "source.txt" in binary mode for reading
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Bopen "source.txt" in binary mode for reading and writing
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CCreate a new file "source.txt" for reading and writing
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DNone of above
Answer
Correct Answer: open "source.txt" in binary mode for reading
Explanation
Introduction / Context:The fopen mode string controls how a file is opened—text vs binary, reading vs writing, appending, and whether a new file is created or an existing one is truncated. Choosing the correct mode avoids data loss and platform-specific newline translations.
Given Data / Assumptions:
- Call shown: fopen("source.txt", "rb").
- Standard C fopen modes apply.
- We aim to interpret the two-character mode "rb".
Concept / Approach:
- "r" means open existing file for reading.
- "b" means binary mode (no text translations such as CRLF to LF on Windows).
- To read and write, modes like "rb+" or "r+b" are used; to create/truncate for writing, use "w" variants.
Step-by-Step Solution:
Parse "r" → open for reading only.Parse "b" → open in binary mode (no newline conversion).Therefore, "rb" means open in binary mode for reading.Verification / Alternative check:
If the intent were read/write, "rb+" would be required; if write/truncate, "wb" would be used.Why Other Options Are Wrong:
- Binary read/write: Requires "+" in the mode.
- Create for read/write: That is "wb+" or "w+b", not "rb".
- None of above: Incorrect because option A is accurate.
Common Pitfalls:
- Opening text files in text mode on Windows and being surprised by newline translation; use "b" for binary data.
- Forgetting that "r" fails if the file does not exist.
Final Answer:
open "source.txt" in binary mode for reading