C, memory and debugging: interview prep

Interview questions

Key points for each answer are in the app's question bank.

1. Explain the difference between const int *p, int *const p and const int *const p.Basic
2. What does volatile do? Give two embedded situations where you need it.Basic
3. What does static mean on a local variable, a global variable and a function?Basic
4. Why does a compiler add padding to structs? How do you minimise it?Intermediate
5. Write a function that detects whether the CPU is little-endian.Basic
6. Write a function to swap the byte order of a 32-bit value.Basic
7. Write macros or inline functions to set, clear, toggle and test bit n of a register.Basic
8. Count the set bits in a 32-bit integer. Give two approaches.Basic
9. How do you check if an unsigned number is a power of two in one expression?Basic
10. Reverse the bits of a byte efficiently.Intermediate
11. Implement memcpy. Then explain how memmove differs and implement it.Intermediate
12. Why is strcpy dangerous? What would you use instead?Basic
13. What are dangling pointers, memory leaks and double frees? How do you prevent them in firmware?Basic
14. Where do local variables, globals, static locals, string literals and malloc'd memory live?Basic
15. What happens on an MCU between reset and main()?Intermediate
16. Use function pointers to implement a table-driven state machine.Intermediate
17. What's wrong with #define SQUARE(x) x*x? Fix it.Basic
18. Compare inline functions and macros.Basic
19. What does if (-1 < sizeof(int)) evaluate to, and why?Intermediate
20. Give three examples of undefined behaviour in C that bite embedded code.Intermediate
21. Implement a fixed-size circular buffer with put and get.Basic
22. Reverse a singly linked list, then detect whether it has a loop.Intermediate
23. When would you use a union in firmware, and what are the caveats?Intermediate
24. Why are C bit-fields risky for mapping hardware registers?Intermediate
25. What are .text, .data, .bss and .rodata, and what does a linker script do?Intermediate
26. Explain extern and why you get multiple-definition linker errors.Basic
27. Implement atoi with error handling for overflow and invalid characters.Intermediate
28. Why is recursion usually avoided on microcontrollers?Intermediate
29. How do hardware and software breakpoints differ?Intermediate
30. A Cortex-M device hits a HardFault in the field. How do you find the cause?Advanced
31. What's the size of a pointer on a 32-bit MCU, and what does sizeof return for an array passed to a function?Intermediate
32. Code works at -O0 but fails at -O2. List the usual causes.Advanced

Hands-on challenges

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