Concatenating TFields values - c++

Question

I have a calculated fields in a client dataset named full address of type Memo.
I want to concatenate address fields, something like this:
TField* f = customersCDS->FieldByName("full_address");
if(f)
{
f->Value = customersCDS->FieldByName("address_line1")->Value;
f->Value += "\n";
f->Value += customersCDS->FieldByName("address_line2")->Value;
..
}
However, the above don't work. I get compiler error:
E2015 Ambiguity between '_fastcall operator Variant::float() const' and '_fastcall operator Variant::double() const'
In the end, I want to bind the calculated field with a TMemo, showing the full address on multiple lines.

Answer 1

TField::Value is a property. You cannot use compound assignment operators, like +=, with properties. You have to use + and = separately, eg:
TField* f = customersCDS->FieldByName("full_address");
if (f)
{
f->Value = customersCDS->FieldByName("address_line1")->Value;
f->Value = f->Value + String("\n");
f->Value = f->Value + customersCDS->FieldByName("address_line2")->Value;
..
}
In which case, you are better off using a variable instead:
TField* f = customersCDS->FieldByName("full_address");
if (f)
{
String s = customersCDS->FieldByName("address_line1")->Value;
s += "\n";
s += customersCDS->FieldByName("address_line2")->Value;
//...
f->Value = s;
}