C typedef with struct tag reuse: Will the following declaration compile and work as intended, creating both a struct tag and a typedef of the same name? typedef struct s { int a; float b; } s;
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AYes; the struct tag namespace is distinct from the typedef namespace, so this is valid.
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BNo; using the same name is a redefinition error.
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COnly in C++; C forbids this.
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DWorks only if a is declared before b.
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EValid only on 64-bit systems.
Answer
Correct Answer: Yes; the struct tag namespace is distinct from the typedef namespace, so this is valid.
Explanation
Introduction / Context: C maintains separate namespaces for struct/union/enum tags and for ordinary identifiers (including typedef names). This question clarifies whether a struct tag and a typedef may share the same spelling.
Given Data / Assumptions:
- Declaration uses both a struct tag `s` and a typedef name `s` in the same statement.
Concept / Approach: The code declares a tag named `s` and simultaneously introduces a typedef name `s` that aliases `struct s`. Because tags and typedef names are in different namespaces, this is valid and common in C. Afterward, you can write `s var;` instead of `struct s var;`.
Step-by-Step Solution: 1) Parse the declaration: it defines `struct s { ... };`. 2) The trailing `} s;` introduces a typedef name `s` that refers to `struct s`. 3) The two uses of `s` live in different namespaces and do not conflict. 4) Using `s x;` now refers to the typedef type.
Verification / Alternative check: Most codebases and textbooks demonstrate this idiom; it compiles cleanly on conforming C compilers.
Why Other Options Are Wrong: Option B: Misinterprets namespaces; no redefinition here. Option C: Works in both C and C++. Option D/E: Member order or machine word size is irrelevant.
Common Pitfalls: Confusing tag and typedef namespaces; thinking the second `s` shadows the first; assuming an ODR-like rule applies in C.
Final Answer: Yes—valid and idiomatic; tag and typedef live in different namespaces.