Getting a string which ends with a string "lngt" in Lex - lex

Question

I am writing a lex script to tokenize C ASTs. I want to write a regex in lex to get a string that ends with a specific string "lngt" but does not include "lngt" in the final string returned by lex. So basically the string form would be (.*lngt), but I haven't been able to figure out how to do this in lex. Any advice/direction would be really helpful
Example:I have this line in my file
#65 string_cst type: #71 strg: Reverse order of the given number is : %d lngt: 42
I want to retrieve string after strg: and before lngt: ie "Reverse order of the given number is : %d" (NOTE: this string could be composed of any characters possible)
Thanks.

Answer 1

This question needs an answer is similar to the one I wrote here. It can be done by writing your own state machine in lex. It could also be done by writing some C code as shown in the cited answer or in the other texts cited below.
If we assume that the string you want is always between "strg" and "lngt" then this is the same as any other non-symmetric string delimiters.
%x STRG LETTERL LN LNG LNGT
ws [ \t\r\n]+
%%
<INITIAL>"strg: " {
BEGIN(STRG);
}
<STRG>[^l]*l {
yymore();
BEGIN(LETTERL);
}
<LETTERL>n {
yymore();
BEGIN(LN);
}
<LN>g {
yymore();
BEGIN(LNG);
}
<LNG>t {
yymore();
BEGIN(LNGT);
}
<LNGT>":" {
printf("String is '%s'\n", yytext);
BEGIN(INITIAL);
}
<LETTERL>[^n] {
BEGIN(STRG);
yymore();
}
<LN>[^g] {
BEGIN(STRG);
yymore();
}
<LNG>[^t] {
BEGIN(STRG);
yymore();
}
<LNGT>[^:] {
BEGIN(STRG);
yymore();
}
<INITIAL>{ws} /* skip */ ;
<INITIAL>. /* skip anything not in the string */
%%
To quote my other answer:
There are suggested solutions on several university compiler courses. The one that explains it well is here (at Manchester). Which cites a couple of good books which also cover the problems:
J.Levine, T.Mason & D.Brown: Lex and Yacc (2nd ed.)
M.E.Lesk & E.Schmidt: Lex - A Lexical Analyzer Generator
The two techniques described are to use Start Conditions to explicity specify the state machine, or manual input to read characters directly.