Find out if a string contains only ASCII characters - regex

Question

I need to know whether a string contains only ASCII characters. So far I use this REGEX:
DECLARE
str VARCHAR2(100) := 'xyz';
BEGIN
IF REGEXP_LIKE(str, '^[ -~]+$') THEN
DBMS_OUTPUT.PUT_LINE('Pure ASCII');
END IF;
END;
/
Pure ASCII
' ' and ~ are the first, resp. last character in ASCII.
Problem is, this REGEXP_LIKE fails on certain NLS-Settings:
ALTER SESSION SET NLS_SORT = 'GERMAN';
DECLARE
str VARCHAR2(100) := 'xyz';
BEGIN
IF REGEXP_LIKE(str, '^[ -~]+$') THEN
DBMS_OUTPUT.PUT_LINE('Pure ASCII');
END IF;
END;
/
ORA-12728: invalid range in regular expression
ORA-06512: at line 4
Do anybody knows a solution which works independently from current user NLS-Settings? Is this behavior on purpose or should it be considered as a bug?

Answer 1

You can use TRANSLATE to do this. Basically, translate away all the ASCII printable characters (there aren't that many of them) and see what you have left.
Here is a query that does it:
WITH input ( p_string_to_test) AS (
SELECT 'This this string' FROM DUAL UNION ALL
SELECT 'Test this ' || CHR(7) || ' string too!' FROM DUAL UNION ALL
SELECT 'xxx' FROM DUAL)
SELECT p_string_to_test,
case when translate(p_string_to_test,
chr(0) || q'[ !"#$%&'()*+,-./0123456789:;<=>?#ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~]',
chr(0)) is null then 'Yes' else 'No' END is_ascii
FROM input;
+-------------------------+----------+
| P_STRING_TO_TEST | IS_ASCII |
+-------------------------+----------+
| This this string | Yes |
| Test this string too! | No |
| xxx | Yes |
+-------------------------+----------+

Answer 2

ASCII function with upper limit of 127 may be used :
declare
str nvarchar2(100) := '\xyz~*-=)(/&%+$#£>|"éß';
a nvarchar2(1);
b number := 0;
begin
for i in 1..length(str)
loop
a := substrc(str,i,1);
b := greatest(ascii(a),b);
end loop;
if b < 128 then
dbms_output.put_line('String is composed of Pure ASCII characters');
else
dbms_output.put_line('String has non-ASCII characters');
end if;
end;

Answer 3

I think I will go for one of these two
IF CONVERT(str, 'US7ASCII') = str THEN
DBMS_OUTPUT.PUT_LINE('Pure ASCII');
END IF;
IF ASCIISTR(REPLACE(str, '\', '/')) = REPLACE(str, '\', '/') THEN
DBMS_OUTPUT.PUT_LINE('Pure ASCII');
END IF;