gcc - yywrap() 在 flex 中的含义

Question

这个指令在 flex (lex) 中是什么意思:
#define yywrap() 1
而这 [\t]+$
我在下面的代码中找到它:

( %%
[ \t]+ putchar('_');
[ \t]+%
%%
输入“ Hello World ”

输出“hello_world”

)

Answer 1

根据 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.

#define用于简化程序的构建(因此不需要 -ll 链接选项)。

进一步阅读:

What are lex and yacc?

Routines to reprocess input

6. How do Lex and YACC work internally (Lex 和 YACC 入门/HOWTO)