The substring function returns the
substring of the first argument starting at the position specified in
the second argument with length specified in the third argument. For
example,
substring("12345",2,3)
returns "234"
.
If the third argument is not specified, it returns the substring
starting at the position specified in the second argument and
continuing to the end of the string. For example,
substring("12345",2)
returns "2345"
.
More precisely, each character in the string (see [3.6 Strings]) is considered to have a
numeric position: the position of the first character is 1, the
position of the second character is 2 and so on.
NOTE: This differs from Java and ECMAScript, in
which the String.substring
method treats the position
of the first character as 0.
The returned substring contains those characters for which the
position of the character is greater than or equal to the rounded
value of the second argument and, if the third argument is specified,
less than the sum of the rounded value of the second argument and the
rounded value of the third argument; the comparisons and addition
used for the above follow the standard IEEE 754 rules; rounding is
done as if by a call to the round
function. The following examples illustrate various unusual cases:
-
substring("12345", 1.5, 2.6)
returns
"234"
-
substring("12345", 0, 3)
returns "12"
-
substring("12345", 0 div 0, 3)
returns ""
-
.
substring("12345", 1, 0 div 0)
returns
""
-
substring("12345", -42, 1 div 0)
returns
"12345"
-
substring("12345", -1 div 0, 1 div 0)
returns
""