How to get such pattern matching of regular expression in lex

问题

Hi I want to check a specific pattern in regular expression but I'm failed to do that. Input should be like

noun wordname:wordmeaning

I'm successful getting noun and wordname but couldn't design a pattern for word meaning. My code is :

int state;
char *meaning;
char *wordd; 

^verb   { state=VERB; }
^adj    { state = ADJ; }
^adv    { state = ADV; }
^noun   { state = NOUN; }
^prep   { state = PREP; }
^pron   { state = PRON; }
^conj   { state = CONJ; }

//my try but failed
[:\a-z]   {
meaning=yytext;
printf(" Meaning is getting detected %s", meaning);

}

[a-zA-Z]+  {
word=yytext;

}

Example input:

noun john:This is a name

Now word should be equal to john and meaning should be equal to This is a name.

回答1:

Agreeing that lex states (also known as start conditions) are the way to go (odd, but there are no useful tutorials).

Briefly:

your application can be organized as states, using one for "noun", one for "john" and one for the definition (after the colon).
at the top of the lex file, declare the states, e.g.,

%s TYPE NAME VALUE
the capitals are not necessary, but since you are defining constants, that is a good convention.
next to the patterns, put those state names in < > brackets to tell lex that the patterns are used only in those states. You can list more than one state, comma-separated, when it matters. But your lex file probably does not need that.
one state is predefined: INITIAL.
your program switches states using the BEGIN() macro, in actions, e.g.,

{ BEGIN(TYPE); }
if your input is well-formed, it's simple: as each "type" is recognized, it begins the NAME state.
in the NAME state, your lexer looks for whatever you think a name should be, e.g.,

<NAME>[[:alpha:]][[:alnum:]]+ { my_name = strdup(yytext); }
the name ends with a colon, so

<NAME>":" { BEGIN(VALUE); }
the value is then everything until the end of the line, e.g.,

<VALUE>.* { my_value = strdup(yytext); BEGIN(INITIAL); }
whether you switch to INITIAL or TYPE depends on what other things you might add to your lexer (such as ignoring comment lines and whitespace).