Advanced C test (Advanced)

Sample questions

5 sample questions from the Advanced C test, with the answers. Samples are taken out of the live test, so you will not meet these when you sit it.

1. What is a potential issue with using bitfields in C when dealing with different compilers or platforms?

   1. The structure's memory layout may vary between compilers/platforms, leading to portability issues.
   2. Bitfield members are always packed tightly without padding, ensuring consistent memory layout.
   3. Bitfield alignment is standardized in the C language and does not vary between compilers.
   4. Bitfields are guaranteed to be aligned to the same boundary as the largest member in the structure.

   Answer: A. The structure's memory layout may vary between compilers/platforms, leading to portability issues.

   Bitfields in C are subject to alignment rules based on the compiler and target platform. This can lead to unexpected memory layouts, which may cause portability issues if not handled carefully. The other options either describe unrelated issues or are not directly related to the specific problem caused by bitfield alignment.

2. Consider two struct definitions: Struct A has padding for alignment, and Struct B has no padding. Which statement best describes their respective use cases?

   1. Struct A is more efficient for frequent access, while Struct B is better for memory alignment in arrays.
   2. Struct B is more efficient for array storage, while Struct A is better for individual access.
   3. Struct A is more efficient for array storage, while Struct B is better for individual access.
   4. Struct A is better for memory alignment, while Struct B is better for performance.

   Answer: A. Struct A is more efficient for frequent access, while Struct B is better for memory alignment in arrays.

   Struct A, with padding for alignment, ensures faster access by the CPU. Struct B, with no padding, aligns better in arrays, reducing wasted space. Struct A is better for performance in individual accesses, while Struct B is better for arrays of structs.

3. Which of the following statements accurately describes a capability of the linker related to performance optimization?

   1. The linker can dynamically load shared libraries during program execution.
   2. The linker is not involved in the optimization of code for performance.
   3. The linker is responsible for resolving external symbol references at runtime.
   4. The linker can optimize the placement of code and data to reduce memory footprint and improve cache performance.

   Answer: D. The linker can optimize the placement of code and data to reduce memory footprint and improve cache performance.

   The linker is responsible for combining object files and libraries into a single executable. During this process, it can perform various optimizations such as dead code elimination, section merging, and layout optimization. These optimizations help reduce the memory footprint of the final executable and improve cache performance by arranging code and data in a way that minimizes cache misses. Other options are incorrect because they either describe unrelated linker behaviors or are not accurate representations of what the linker can do.

4. What happens when a signal is used for inter-process communication (IPC) and the receiving process is not in a state to handle it immediately?

   1. The signal is ignored by the operating system and not delivered to any process.
   2. The signal is delivered to the receiving process, but the process may not handle it immediately.
   3. The signal is delivered to the sending process instead of the receiving process.
   4. The signal is always handled immediately by the receiving process.

   Answer: B. The signal is delivered to the receiving process, but the process may not handle it immediately.

   When a signal is sent to a process using inter-process communication (IPC), it is queued and delivered to the receiving process. However, the receiving process may not handle the signal immediately, depending on its current state and signal handling configuration. This behavior is different from synchronous IPC mechanisms like pipes or message queues, where the sender may block until the receiver processes the message.

5. Which approach correctly manages symbol linkage in C for internal vs. external visibility?

   1. Use `extern` for internal linkage and `static` for external linkage.
   2. Use `extern` for external linkage and `static` for internal linkage.
   3. Use `static` to alias symbols across translation units.
   4. Use `static` for both internal and external linkage.

   Answer: B. Use `extern` for external linkage and `static` for internal linkage.

   In C, `static` at the file scope provides internal linkage, meaning the symbol is visible only within the translation unit. `extern` declares a symbol with external linkage, making it visible across translation units. This distinction is crucial for controlling symbol visibility and aliasing during linking.