Handling Errors in Lexical Analysis MCQs
What is the primary purpose of error handling in lexical analysis?
A) To ignore syntax errors
B) To identify and report issues in the token stream
C) To optimize the performance of the lexer
D) To generate debugging information
Answer: B
Which function is typically used to report errors in Lex?
A) yyerror()
B) yylex()
C) yywrap()
D) yyinput()
Answer: A
In Lex, how can you define a custom error handling function?
A) By implementing yyerror()
B) By modifying yylex()
C) By configuring the -e option
D) By using the %error directive
Answer: A
What is the purpose of the yytext variable in error handling?
A) It stores the text of the current token, useful for error reporting
B) It manages the state of the lexer
C) It determines the type of error
D) It sets the length of the token
Answer: A
How does Lex handle invalid or unrecognized characters by default?
A) By generating an error message
B) By ignoring them
C) By treating them as whitespace
D) By stopping the lexical analysis
Answer: A
Which special pattern can be used to handle errors in Lex?
A) %%
B) <<EOF>>
C) . (dot)
D) error
Answer: D
What does the error pattern in Lex do?
A) It matches any character that is not matched by other patterns
B) It reports syntax errors
C) It handles end-of-file conditions
D) It resets the lexer state
Answer: A
Which Lex function can be used to skip over unrecognized input?
A) yyrestart()
B) yylex()
C) yywrap()
D) yyless()
Answer: D
What is the role of the yywrap() function in error handling?
A) To handle the end of the input file and reset the lexer
B) To initialize the lexer state
C) To parse and validate tokens
D) To manage syntax errors
Answer: A
How can you include error messages in the action code of a Lex rule?
A) By using the fprintf(stderr, …) function
B) By modifying the yyerror() function
C) By setting the -e option
D) By using Lex directives
Answer: A
In Lex, which function should be implemented to handle errors during lexical analysis?
A) yyerror()
B) yylex()
C) yywrap()
D) yyinit()
Answer: A
What is the purpose of yylval in the context of lexical errors?
A) It stores the value associated with a token, useful for error reporting
B) It holds the length of the matched text
C) It manages the input stream
D) It initializes the lexer
Answer: A
How do you handle unexpected characters in a Lex specification?
A) By defining an error pattern in the rules section
B) By modifying the yytext variable
C) By configuring Lex options
D) By writing custom parsing code
Answer: A
What does the yytext variable contain when an error is detected?
A) The unrecognized input that caused the error
B) The previous token
C) The length of the token
D) The error message
Answer: A
How can you handle end-of-file (EOF) conditions gracefully in Lex?
A) By implementing yywrap()
B) By using the <<EOF>> pattern
C) By configuring the -e option
D) By writing custom error handling code
Answer: A
What is the purpose of the yyleng variable in Lex?
A) To hold the length of the matched text
B) To store the current line number
C) To manage the input stream
D) To track the number of errors
Answer: A
How can Lex be configured to produce error messages for invalid tokens?
A) By using the error pattern with fprintf(stderr, …)
B) By modifying the yywrap() function
C) By setting Lex options
D) By defining custom patterns
Answer: A
Which pattern in Lex is used to match any character that does not match other patterns?
A) error
B) .*
C) [^\s]
D) <<EOF>>
Answer: A
What should be done if yyerror() is not implemented?
A) The lexical analyzer will not report errors, which may lead to unhandled situations
B) Lex will automatically generate a default error handler
C) The analyzer will terminate without processing tokens
D) The analyzer will skip over errors without reporting them
Answer: A
How do you handle errors related to input that is too long for a token in Lex?
A) By using the yyless() function to process the excess input
B) By configuring the -l option
C) By defining a pattern for long tokens
D) By adjusting the buffer size
Answer: A
What is the effect of an undefined pattern in Lex?
A) It triggers the error pattern
B) It causes Lex to stop processing
C) It generates a default token
D) It is ignored
Answer: A
In Lex, how can you handle errors and continue processing?
A) By using the error pattern to skip invalid input
B) By terminating the lexer
C) By setting the -c option
D) By modifying the yywrap() function
Answer: A
How can you ensure that errors are reported in the context of a specific line number?
A) By using the yytext and yylineno variables together
B) By configuring Lex options for line numbering
C) By setting up custom error handling functions
D) By including line numbers in error messages
Answer: A
What is a common practice for handling lexical errors in a production environment?
A) Logging errors to a file for later analysis
B) Ignoring errors to ensure smooth operation
C) Terminating the process on the first error
D) Displaying error messages directly to users
Answer: A
In Lex, how do you reset the input stream to handle new input files?
A) By using yyrestart()
B) By modifying yywrap()
C) By using the -r option
D) By reinitializing yytext
Answer: A
What is the role of the yytext variable in custom error handling?
A) To provide the text of the token that caused the error
B) To manage the length of tokens
C) To track the position in the input file
D) To configure error reporting settings
Answer: A
How can you handle errors when the input is malformed but still needs to be processed?
A) By using yyless() to adjust the input
B) By using the error pattern to skip malformed input
C) By terminating the lexer and reporting errors
D) By adjusting buffer sizes
Answer: B
Which Lex function is used to handle end-of-file (EOF) conditions without generating errors?
A) yywrap()
B) yyerror()
C) yylex()
D) yyrestart()
Answer: A
How does Lex handle patterns that overlap with the error pattern?
A) The error pattern takes precedence
B) Lex reports an error and stops processing
C) The first matching pattern is used
D) Lex generates a default error message
Answer: C
What should be done if an error is detected but cannot be recovered?
A) Log the error and terminate the processing
B) Ignore the error and continue processing
C) Automatically correct the input
D) Skip the erroneous token
Answer: A
In Lex, which variable tracks the current position in the input stream?
A) yytext
B) yylineno
C) yypos
D) yyfile
Answer: B
How can you provide detailed error reporting in Lex?
A) By customizing the yyerror() function
B) By using the error pattern
C) By configuring Lex options for verbosity
D) By including error details in the yylex() function
Answer: A
What is the effect of not handling errors explicitly in Lex?
A) Lex may produce incorrect tokens or terminate unexpectedly
B) Lex will automatically correct input errors
C) Lex will ignore all errors and continue processing
D) Lex will generate default error messages
Answer: A
What does the yyless(n) function do in relation to error handling?
A) It discards n characters from the current token to handle errors
B) It sets the length of the current token to n
C) It resets the lexer to the state before the last token
D) It reports an error if the token length exceeds n
Answer: A
Which of the following is an appropriate way to handle unexpected end-of-file conditions?
A) Implement yywrap() to manage EOF
B) Use the <<EOF>> pattern
C) Configure Lex options for EOF handling
D) Modify the yylex() function
Answer: A
How can Lex be configured to provide more informative error messages?
A) By customizing the yyerror() function to include specific details
B) By setting the -v option
C) By adjusting the error pattern
D) By configuring buffer sizes
Answer: A
In Lex, what should you do if an error is detected in the middle of a token?
A) Use yyless() to adjust the token and handle the error
B) Terminate the lexer and report an error
C) Skip the entire token and continue processing
D) Correct the input automatically
Answer: A
What is the purpose of including error handling code in the Lex specification?
A) To manage and report errors effectively during lexical analysis
B) To optimize token generation
C) To configure the input stream
D) To set buffer sizes
Answer: A
How does Lex handle overlapping patterns when an error occurs?
A) The longest matching pattern is used
B) Lex uses the first matching pattern
C) Lex generates a default error message
D) The error pattern takes precedence
Answer: A
Which function in Lex is responsible for handling token values and errors?
A) yyerror()
B) yylex()
C) yywrap()
D) yyinput()
Answer: A
How can you handle errors in Lex when the input is too large to process?
A) By using the yyless() function to manage excess input
B) By adjusting the buffer size
C) By configuring Lex options for large input
D) By skipping large input segments
Answer: A
What does the yyrestart() function do in Lex?
A) It resets the lexer to handle new input files
B) It initializes error handling
C) It manages token values
D) It processes end-of-file conditions
Answer: A
How should you handle errors related to incorrect token values in Lex?
A) By using the error pattern to report issues
B) By modifying the yytext variable
C) By adjusting buffer sizes
D) By using custom token values
Answer: A
What does the yylineno variable represent in error handling?
A) The current line number in the input file
B) The length of the matched token
C) The position of the error in the token
D) The number of errors encountered
Answer: A
How can you ensure that errors are properly handled when using Lex with Yacc?
A) By coordinating error handling between Lex and Yacc
B) By using default error handling functions
C) By configuring Lex and Yacc separately
D) By modifying Yacc to handle Lex errors
Answer: A
What is the purpose of including error handling in the action code of a Lex rule?
A) To report and manage errors in the matched tokens
B) To optimize token generation
C) To configure input and output settings
D) To adjust buffer sizes
Answer: A
How can Lex handle errors when encountering end-of-file (EOF) in the middle of processing?
A) By implementing yywrap() to handle EOF conditions
B) By using the error pattern to manage EOF
C) By modifying the yytext variable
D) By skipping EOF conditions
Answer: A
What should be done if a Lex specification needs to handle errors for specific patterns only?
A) Define custom error handling for those patterns
B) Use the default error pattern for all errors
C) Skip patterns with errors
D) Configure Lex options for pattern-specific errors
Answer: A
Which approach is best for handling complex error scenarios in Lex?
A) Implementing a detailed yyerror() function
B) Using simple error patterns
C) Ignoring errors
D) Relying on default error handling
Answer: A
How does Lex handle errors when the input is not well-formed according to the defined patterns?
A) By using the error pattern to handle and report the invalid input
B) By generating default tokens
C) By terminating the analysis
D) By skipping over invalid input
Answer: A