Have problem with lex

问题:

My lex as follows:

LNUM    [0-9]+
DNUM([0-9]*"."[0-9]+)|([0-9]+"."[0-9]*)                                                                                    
%%
{LNUM} {
printf("\t");ECHO;printf("\r\n");
}

{DNUM} {
printf("\t");ECHO;printf("\r\n");
}

But it turns out that it can only match numbers like 4.12 .2,not 42,45. etc.(those indented are matched)

Output:

1.
1.
.1
    .1

12
12

My target is to match both integers and float numbers.

Can anyone here tell me what's wrong above?

回答1:

Late answer to your question... but for what it's worth, I tried replacing the * you had in the original lex file (the second pattern for DNUM) with a + (because that ensures that you at least have one digit to the right of the decimal point in order for the number to be counted as a decimal...) and it seems to work for me, at least. Hope this helps someone in the future.

---

lex file:

%{
#include <iostream>
using namespace std;
%}

LNUM    [0-9]+
DNUM    ([0-9]*"."[0-9]+)|([0-9]+"."[0-9]+) 

%option noyywrap

%%
{LNUM}*  { cout << "lnum: " << yytext << endl; }
{DNUM}*  { cout << "dnum: " << yytext << endl; }
%%

int main(int argc, char ** argv)
{
    yylex();
    return 0;
}

---

example input (on command line):

$ echo "4.12 .2 42 45. " | ./lexer
dnum: 4.12
dnum: .2
lnum: 42
lnum: 45.