![]() ![]() Each action fragment can call actions or subroutines outside of itself. These actions are C language program fragments in the lex specification file. ![]() Executes an action for each extended regular expression that it recognizes.Breaks the input stream into smaller strings that match the extended regular expressions in the lex specification file.Copies the input stream to an output stream.The compiled lexical analyzer performs the following functions: You can move a lex.yy.c output file to another system if it has C compiler that supports the lex library functions. However, if the lexical analyzer must recognize more complex syntax, you can create a parser program to use with the output file to ensure proper handling of any input. If the output program recognizes a simple, one-word input structure, you can compile the lex.yy.c output file with the following command to get an executable lexical analyzer: cc lex.yy.c -ll The lex command then stores the output program in a lex.yy.c file. The lex command generates a C language program that can analyze an input stream using information in the specification file. The format and logic allowed in this file are discussed in the lex Specification File section of the lex command. To use the lex command, you must supply or write a specification file that contains: Extended regular expressionsĬharacter patterns that the generated lexical analyzer recognizes.Ĭ language program fragments that define how the generated lexical analyzer reacts to extended regular expressions it recognizes. The lex command helps write a C language program that can receive and translate character-stream input into program actions. Writing a Lexical Analyzer Program with the lex Command Generates a parser program that analyzes input using the tokens identified by the lexical analyzer (generated by the lex command and stored in the lex specification file) and performs specified actions, such as flagging improper syntax. ![]() ![]() The tokens are defined by grammar rules set up in the lex specification file. Generates a lexical analyzer program that analyzes input and breaks it into tokens, such as numbers, letters, or operators. You can use the lex and yacc commands to develop this type of input program. Complicated input requires additional code to break the input into pieces that mean something to the program. Creating an Input Language with the lex and yacc CommandsĪIX Version 4.3 General Programming Concepts: Writing and Debugging Programsįor a program to receive input, either interactively or in a batch environment, you must provide another program or a routine to receive the input. ![]()
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