MCQs on Error Handling and Debugging | Lua

1. Error Handling with pcall and xpcall

1. What does the pcall function do in Lua?
   • a) Executes a function in protected mode
   • b) Prints error messages
   • c) Pauses the execution of the program
   • d) None of the above
2. How does xpcall differ from pcall in Lua?
   • a) xpcall uses a custom error handler
   • b) xpcall does not handle errors
   • c) pcall uses a custom error handler
   • d) There is no difference between xpcall and pcall
3. What is the primary advantage of using pcall over a simple function call in Lua?
   • a) It ensures that any errors do not stop the program
   • b) It improves the performance of the program
   • c) It automatically logs the errors
   • d) It reduces memory consumption
4. What type of value does pcall return when the function executes successfully?
   • a) true and the function’s result
   • b) false and the error message
   • c) true and an error message
   • d) false and the function’s result
5. Which of the following is true about xpcall in Lua?
   • a) It provides a way to handle errors with a custom error handler
   • b) It throws an error and exits the program
   • c) It automatically handles all errors without needing a handler
   • d) It returns only the error message without the error status
6. In Lua, what happens if a function inside pcall throws an error?
   • a) The error is caught and handled gracefully
   • b) The program halts without any error message
   • c) The error is thrown to the global scope
   • d) The error is printed to the console
7. Which of the following is a valid use case for xpcall?
   • a) To catch errors and provide a custom error handler
   • b) To execute multiple functions simultaneously
   • c) To call functions asynchronously
   • d) To prevent a function from returning any value
8. What is required as the second argument in xpcall?
   • a) A function to handle the error
   • b) A string containing the error message
   • c) A custom debug function
   • d) A table of error types
9. What would happen if you call pcall with a function that always throws an error?
   • a) pcall will return false and the error message
   • b) The error will be displayed and program execution stops
   • c) It will cause an infinite loop
   • d) It will cause the function to retry automatically
10. How do you use pcall to handle errors in Lua?
    • a) By wrapping the function call inside pcall
    • b) By manually checking for errors after every function call
    • c) By using the assert function
    • d) By using pcall only in loops

2. Using error() and assert()

11. What is the purpose of the error() function in Lua?
    • a) To raise an error with a custom message
    • b) To suppress an error
    • c) To log errors to a file
    • d) To ignore errors
12. What does the assert() function do in Lua?
    • a) It raises an error if the condition is false
    • b) It catches all errors and prints a message
    • c) It forces the program to exit
    • d) It throws an error if the condition is true
13. In Lua, what happens when assert() is given a false condition?
    • a) It raises an error with the provided message
    • b) It returns false
    • c) It prints a warning message
    • d) It does nothing
14. What is the output of assert(false, "Error occurred") in Lua?
    • a) The function throws an error with the message “Error occurred”
    • b) The function returns false
    • c) The program continues without interruption
    • d) It prints “Error occurred” to the console
15. How can error() be used to specify the level of the error in Lua?
    • a) By passing an integer level argument after the message
    • b) By passing a string containing the error level
    • c) By calling error() inside a loop
    • d) Lua does not allow specifying the level of the error
16. What does assert() return if the condition is true?
    • a) The condition itself
    • b) nil
    • c) The argument provided to assert()
    • d) It returns the function that called assert()
17. What is the function signature of error() in Lua?
    • a) error(message, level)
    • b) error(level, message)
    • c) error(message)
    • d) error()
18. How does assert() handle the message parameter when the condition is true?
    • a) It ignores the message
    • b) It prints the message
    • c) It returns the message as a string
    • d) It throws the message as an exception
19. Can you use error() to raise a custom error message in Lua?
    • a) Yes, by passing a string as an argument
    • b) No, error() can only print default messages
    • c) Yes, but it only works for system errors
    • d) No, error() does not support custom messages
20. How would you use assert() to ensure a variable x is not nil?
    • a) assert(x, "x cannot be nil")
    • b) assert(x == nil)
    • c) assert(x ~= nil, "x cannot be nil")
    • d) assert(x)

3. Introduction to the Debug Library

21. What is the main purpose of the Lua debug library?
    • a) To enable the inspection and manipulation of program execution
    • b) To handle errors and exceptions
    • c) To improve program performance
    • d) To generate reports on program usage
22. Which function from the debug library is used to get the stack trace in Lua?
    • a) debug.traceback
    • b) debug.getstack
    • c) debug.getinfo
    • d) debug.showstack
23. What does the debug.getinfo() function return in Lua?
    • a) Information about a function or its execution context
    • b) The current stack trace
    • c) The global variables used in the function
    • d) The memory usage of the function
24. Which function would you use to set a hook for debugging in Lua?
    • a) debug.sethook
    • b) debug.settrace
    • c) debug.trace
    • d) debug.gethook
25. What does the debug.getlocal() function do in Lua?
    • a) Returns local variables of a function
    • b) Returns the current function name
    • c) Returns the global variables of the program
    • d) Prints the current local variables to the console
26. How would you use debug.traceback() to get a detailed stack trace in Lua?
    • a) By passing the error message as an argument
    • b) By calling it within an error-handling function
    • c) By passing the level argument
    • d) debug.traceback() cannot generate stack traces
27. What is the purpose of debug.sethook() in Lua?
    • a) To monitor function calls and return values
    • b) To log all errors
    • c) To set breakpoints in the code
    • d) To print the stack trace
28. What does debug.getupvalue() return in Lua?
    • a) The upvalue of a function
    • b) The local variable inside the function
    • c) The global variable referenced by the function
    • d) The environment of a function
29. How would you prevent the Lua debugger from showing certain variable values?
    • a) By using debug.sethook() to filter out variables
    • b) By disabling the debug library
    • c) By using debug.sethook() with specific conditions
    • d) The debugger cannot be filtered
30. Which function from the Lua debug library allows you to get the number of function arguments?
    • a) debug.getn()
    • b) debug.getstack()
    • c) debug.getinfo()
    • d) debug.getlocal()

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