Difference between revisions of "Lex Tutorial"
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===The Lex Format=== | ===The Lex Format=== | ||
A Lex program is separated into three sections by '''%%''' delimiters. The format of Lex source is as follows: <br><br> | A Lex program is separated into three sections by '''%%''' delimiters. The format of Lex source is as follows: <br><br> | ||
| − | '''{ definitions }''' | + | '''{ definitions }''' <br> |
%% <br> | %% <br> | ||
'''{ rules }''' <br> | '''{ rules }''' <br> | ||
%% <br> | %% <br> | ||
'''{ user subroutines }''' | '''{ user subroutines }''' | ||
| + | |||
| + | |||
| + | ==== '''Definitions''' ==== | ||
| + | include declarations of '''constant''', '''variable''' and '''regular definitions'''. | ||
Revision as of 01:11, 10 August 2020
Lex
- Lex is a program that generates lexical analyzer. It is used with YACC parser generator.
- The lexical analyzer is a program that transforms an input stream into a sequence of tokens.
- It reads the input stream and produces the source code as output through implementing the lexical analyzer in the C program.
The function of Lex is as follows:
- Firstly lexical analyzer creates a program lex.1 in the Lex language. Then Lex compiler runs the lex.1 program and produces a C program lex.yy.c.
- Finally C compiler runs the lex.yy.c program and produces an object program a.out.
- a.out is lexical analyzer that transforms an input stream into a sequence of tokens.
The Lex Format
A Lex program is separated into three sections by %% delimiters. The format of Lex source is as follows:
{ definitions }
%%
{ rules }
%%
{ user subroutines }
Definitions
include declarations of constant, variable and regular definitions.
