[GitHub] [incubator-doris] morningman commented on a change in pull request #3345: [FIX] fix doris string functions not support multibyte string

[GitBox <gi...@apache.org>]

morningman commented on a change in pull request #3345: [FIX] fix doris string functions not support multibyte string
URL: https://github.com/apache/incubator-doris/pull/3345#discussion_r410261854
 
 

 ##########
 File path: be/src/exprs/string_functions.cpp
 ##########
 @@ -37,19 +37,55 @@ void StringFunctions::init() {
 //  - supported negative positions (count from the end of the string)
 //  - [optional] len.  No len indicates longest substr possible
 StringVal StringFunctions::substring(
-        FunctionContext* context, const StringVal& str, 
+        FunctionContext* context, const StringVal& str,
         const IntVal& pos, const IntVal& len) {
     if (str.is_null || pos.is_null || len.is_null) {
         return StringVal::null();
     }
+    if (len.val <= 0 || str.len == 0) {
+        return StringVal();
+    }
+
+    // create index indicate every char start byte
+    // e.g.  "hello word 你好" => [0,1,2,3,4,5,6,7,8,9,10,11,14] 你 and 好 are 3 bytes
+    // why use a vector as index? if theres is no negative pos val it is unnecessary,
+    // but if has pos is negative it is not easy to determin where to start, so need a 
+    // index save ervery charactor's length
 
 Review comment:
   ```suggestion
       // index save every character's length
   ```

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