What is Yytext used for?
What is Yytext used for?
yytext holds the text matched by the current token. So yytext[0] holds the first character of the text matched by the current token. Sometimes you have a rule which can match different texts so you need to get the real text matched like for variable names or you have a rule to match all arithmetic operations.
What is the function of Yywrap?
A lex library routine that you can redefine is yywrap() , which is called whenever the scanner reaches the end of file. If yywrap() returns 1, the scanner continues with normal wrapup on the end of input.
What is Yytext variable?
Variable yytext is a pointer to the matched string (NULL-terminated) and yyleng is the length of the matched string. Variable yyout is the output file and defaults to stdout . Function yywrap is called by lex when input is exhausted.
What are the lex library function?
lex library
| Subroutine | Description |
|---|---|
| yyless(int n) | Retains n initial characters in the yytext array and returns the remaining characters to the input stream. |
| yyreject() | Allows the lexical analyzer to match multiple rules for the same input string. (The yyreject subroutine is called when the special action REJECT is used.) |
What type is Yytext?
yytext is of type char* and it contains the lexeme currently found. A lexeme is a sequence of characters in the input stream that matches some pattern in the Rules Section.
What does Yytext return?
Added comment by @VSaiNagendra ” yytext contains text matched by the current token. It means yytext[0] returns the first character of the matched token.”
What is the meaning of Yywrap () return 0?
That means “end of file”. If yywrap returns 0, then yylex assumes that you have stored a different file into yyin, and it starts reading that file.
What is input () in Lex?
Input/Output Subroutines The lex program allows a program to use the following input/output (I/O) subroutines: input() Returns the next input character. output(c) Writes the character c on the output.
What is Yylval in lex?
The yylval global variable is used to pass the semantic value associated with a token from the lexer to the parser. The semantic values of symbols are accessed in yacc actions as $1 , $2 , etc and are set for non-terminals by assigning to $$ .
What is input () in lex?
What are the rules for Lex?
In fact, lex provides a macro called ECHO that is equivalent to printf (“%s”, yytext). When your action consists of a long C statement, or two or more C statements, you might write it on several lines. To inform lex that the action is for one rule only, enclose the C code in braces.
Where is Yytext defined?
Note that yytext can be defined in two different ways: either as a character pointer or as a character array. You can control which definition flex uses by including one of the special directives `%pointer’ or `%array’ in the first (definitions) section of your flex input.
How does the yytext array work?
The action uses the lex array yytext [], which stores the recognized character string. The specification uses the * to indicate that zero or more letters can follow the G. Besides storing the matched input text in yytext [], the scanner automatically counts the number of characters in a match and stores it in the variable yyleng.
What does the * mean in yytext [yyleng]?
The specification uses the * to indicate that zero or more letters can follow the G. Besides storing the matched input text in yytext [], the scanner automatically counts the number of characters in a match and stores it in the variable yyleng. You can use this variable to refer to any specific character just placed in the array yytext [].
How does the yylex() function work?
The yylex () as written by Lex reads characters from a FILE * file pointer called yyin. If you do not set yyin, it defaults to standard input. It outputs to yyout, which if unset defaults to stdout.
What is the difference between yytext and yywrap?
Variable yytext is a pointer to the matched string (NULL-terminated) and yyleng is the length of the matched string. Variable yyout is the output file and defaults to stdout. Function yywrap is called by lex when input is exhausted.
