Meaning of yywrap() in flex

gcc compiler-construction compilation flex-lexer lexical-analysis
deep_geek picture deep_geek · Dec 27, 2015 · Viewed 9.8k times · Source

What does this instructions mean in flex (lex) :

#define yywrap() 1

and this [ \t]+$
i find it in the code below:

(%% [ \t]+ putchar('_'); [ \t]+% %%

input "hello world"

output "hello_world"

)

Answer

Thomas Dickey picture Thomas Dickey · Dec 27, 2015

According to The Lex & Yacc Page :

When the scanner receives an end-of-file indication from YY_INPUT, it then checks the yywrap() function. If yywrap() returns false (zero), then it is assumed that the function has gone ahead and set up yyin to point to another input file, and scanning continues. If it returns true (non-zero), then the scanner terminates, returning 0 to its caller. Note that in either case, the start condition remains unchanged; it does not revert to INITIAL.

The #define is used to simplify building the program (so that no -ll linkage option is needed).

Further reading:

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