How does one use REJECT in flex?

Let's be clear I'm talking about the lexical analysis tool.

For the following input:

aa bb cc dd

I need the parser to match the following sub strings:

aa bb

bb cc

cc dd

I have this regex:

[a-zA-Z]+[ ]+[a-zA-Z]+

But this only matches开发者_运维百科:

aa bb

cc dd

I've been told the REJECT command can be used to get the output I need but I don't know how to apply it. Could someone give me a hand?

REJECT will start the scan over, then you just need to "eat" the first alphabetic string that you already matched. Possibly this is what you wanted (10 years ago :-):

%%
[a-zA-Z]+[ ]+[a-zA-Z]+    { printf("found %s\n", yytext); REJECT; }
[a-zA-Z]+[ ]*

Given the input string:

a b c d e

it will produce:

found a b
found b c
found c d
found d e

You can use a regex to enumerate n and n + 1 pairs through an entire set.

Look into a grouping with a "greedy" backwards (or forwards) match.

This is one Flex solution to the problem :

    %%
    "aa bb"         {printf( "matched aa bb\n");REJECT;}
    "bb cc"         {printf( "matched bb cc\n");REJECT;}
    "cc dd"         {printf( "matched cc dd\n");REJECT;}
    .               /*ignore anything else*/
    %%
    int main()
    {
    yylex();
    return 0;
    }


When I run the code on your input I get :
matched aa bb
matched bb cc
matched cc dd