Structures, Unions & Pointers in C: 18 flashcards
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1. What is a structure in C?
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A user-defined data type that groups variables of different types under one name.
2. Which operator accesses members of a structure variable?
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The dot operator (`.`), e.g., `s.roll`.
3. Which operator accesses members through a pointer to a structure?
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The arrow operator (`->`), e.g., `p->roll`.
4. What is `p->member` shorthand for?
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`(*p).member`
5. Why might `sizeof(struct T)` be larger than the sum of its members?
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Because of padding added for memory alignment.
6. How is a union stored in memory?
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All members share the same memory location.
7. What is the size of a union?
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The size of its largest member.
8. How many union members are valid at a time?
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Only one — the last one written.
9. When should you use a union instead of a structure?
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When a variable holds one of several types but never more than one at a time, or to save memory.
10. What is a self-referential structure?
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A structure containing a pointer to its own type, used to build linked lists, trees, etc.
11. What is the safe default for passing large structures to functions?
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Pass by `const` pointer to avoid copying and prevent modification.
12. What happens when you pass a structure by value?
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The entire structure is copied.
13. Why is `*p.member` wrong?
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Because `.` binds tighter than `*`, so it parses as `*(p.member)`, not `(*p).member`.
14. What is a tagged union?
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A structure combining a tag field with a union to represent variant types safely.
15. What is padding in structures?
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Unused bytes inserted between members to satisfy alignment requirements.
16. How can you reduce padding in a structure?
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Reorder members from largest to smallest.
17. Give a practical use of unions in embedded systems.
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Register overlays: same bits accessed as a word or as bytes.
18. What is the result of reading a union member other than the last written?
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The bytes are reinterpreted; the result is not portable and usually not what you want.
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