[GitHub] [arrow-adbc] paleolimbot commented on a diff in pull request #587: refactor(c/driver/common): Variadic arguments for StringBuilderAppend

["paleolimbot (via GitHub)" <gi...@apache.org>]

paleolimbot commented on code in PR #587:
URL: https://github.com/apache/arrow-adbc/pull/587#discussion_r1167221556


##########
c/driver/common/utils.c:
##########
@@ -124,19 +124,33 @@ void StringBuilderInit(struct StringBuilder* builder, size_t initial_size) {
   builder->size = 0;
   builder->capacity = initial_size;
 }
-void StringBuilderAppend(struct StringBuilder* builder, const char* value) {
-  size_t length = strlen(value);
-  size_t new_size = builder->size + length;
-  if (new_size > builder->capacity) {
-    size_t new_capacity = builder->size + length - builder->capacity;
-    if (builder->size == 0) new_capacity++;
-
-    builder->buffer = realloc(builder->buffer, new_capacity);
-    builder->capacity = new_capacity;
+void StringBuilderAppend(struct StringBuilder* builder, const char* fmt, ...) {
+  va_list argptr;
+  char* value;
+
+  va_start(argptr, fmt);

Review Comment:
   Can you use `vsnprintf()` here and nanoarrow's `ArrowBuffer` to simplify anything here? Maybe:
   
   ```c
   int chars_required = vsnprintf(NULL, 0, fmt, va_args);
   ArrowBufferReserve(buffer, chars_required + 1)
   vsnprintf(buffer->data + buffer->size_bytes, chars_required, fmt, va_args);
   buffer->size_bytes += chars_required;
   ```
   
   (Maybe I'm misunderstanding what this does too though...also I forget the exact details of where you have to do + 1 with the return value of vsnprintf)



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