Mikroelektronika MIKROE-350 Fiche De Données

Any item of a regular expression may be followed by another type of metacharac-
ters - iterators. Using this metacharacters,you can specify number of occurences of
previous character, metacharacter or subexpression. 

*

- zero or more ("greedy"), similar to {0,} 

+

- one or more ("greedy"), similar to {1,} 

?

- zero or one ("greedy"), similar to {0,1} 

{n}

- exactly n times ("greedy") 

{n,}

- at least n times ("greedy") 

{n,m}

- at least n but not more than m times ("greedy") 

*?

- zero or more ("non-greedy"), similar to {0,}? 

+?

- one or more ("non-greedy"), similar to {1,}? 

??

- zero or one ("non-greedy"), similar to {0,1}? 

{n}?

- exactly n times ("non-greedy") 

{n,}?

- at least n times ("non-greedy") 

{n,m}?

- at least n but not more than m times ("non-greedy") 

So, digits in curly brackets of the form, 

{n,m}

, specify the minimum number of times to

match the item n and the maximum 

m.

The form 

{n} 

is equivalent to

{n,n} 

and match-

es exactly 

n

times. The form

{n,}

matches 

n

or more times. There is no limit to the size

of 

n

or 

m

, but large numbers will chew up more memory and slow down execution.

If a curly bracket occurs in any other context, it is treated as a regular character.

count.*r ß

- matches strings like 

'counter', 'countelkjdflkj9r'

and 

'countr' 

count.+r

- matches strings like 

'counter', 'countelkjdflkj9r'

but not 

'countr' 

count.?r

- matches strings like 

'counter', 'countar'

and 

'countr'

but not

'countelkj9r'

counte{2}r

- matches string 

'counteer' 

counte{2,}r

- matches strings like 

'counteer', 'counteeer', 'counteeer'

etc. 

counte{2,3}r

- matches strings like 

'counteer'

, or 

'counteeer'

but not 

'coun-

teeeer' 

A little explanation about "greediness". "Greedy" takes as many as possible, "non-
greedy" takes as few as possible. 
For example, 

'b+'

and 

'b*' 

applied to string 

'abbbbc'

return 

'bbbb', 'b+?

'

returns 

'b', 'b*?'

returns empty string,

'b{2,3}?'

returns 

'bb', 'b{2,3}'

returns 

'bbb'

. 

65

- SOFTWARE AND HARDWARE SOLUTIONS FOR EMBEDDED WORLD

CHAPTER 2