Compiler lecture 04
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This document discusses compiler construction and error handling. It describes the basic tasks of an error handler as detection, reporting, and recovery of errors encountered during compilation. Errors are classified and the document focuses on lexical analysis. The lexical analyzer takes source code as character streams and breaks it into tokens based on predefined patterns and grammar rules. It generates errors for invalid tokens and works closely with the syntax analyzer by passing tokenized data.
Compiler lecture 04
- 1. Compiler Construction By Noor wali khan UOCH Continue from Previous Lecture
- 2. Error Handler • An error is an abnormal condition in source program, which either stope the compilation or generate undesired results. • A compiler must not stop at each error. • It must somehow handle the error, so that compilation proceeds up to the end of the program. • At the end a list of errors messages is provided to the user. • This is the job of the error handler, and also marks the place where the errors occur.
- 3. Error Handler • Error handler contains a set of routines for handling error encountered in any phase of the compiler. • The basic tasks of the compiler are: • Detection • Reporting • Recovery • During compilation process each phase may encounters errors and has to deal with them. • For this purpose the Error handler contains error handling routines.
- 5. Lexical analyzer • It is the first phase of compiler. • It is also known as linear analyzer or Scanner. • It scans or reads the source program from left to right as a stream of characters, and it groups these characters into a unit called “Tokens”. OR • It takes the source code program as a stream of characters and broken them into tokens.
- 6. Lexical Analyzer • Token: •A sequence of characters having a collective meaning. •Lexemes are said to be a sequence of characters (alphanumeric) in a token. •If the lexical analyzer finds a token invalid, it generates an error. •There are some predefined rules for every lexeme to be identified as a valid token. •These rules are defined by grammar rules, by means of a pattern.
- 7. Lexical Analyzer (Token Cont.) • A pattern explains what can be a token, and these patterns are defined by means of regular expressions. • In programming language, keywords, constants, identifiers, strings, numbers, operators and punctuations symbols can be considered as tokens For example, in C language, the variable declaration line int value = 100; contains the tokens: int (keyword), value (identifier), = (operator), 100 (constant) and ; (symbol).
- 8. Lexical Analyzer (Token Cont.) • The lexical analyzer works closely with the syntax analyzer. • It reads character streams from the source code, checks for legal tokens, and passes the data to the syntax analyzer when it demands. Continue To Next Lecture