XE2 XML Attribute can't convert to double

Question

I have a XML node with attributes like this:

<pad name="E" x="2.5" y="7" drill="1.3"/>

When I assign the Attributes["x"] into a double I get the result 25, not 2.5 but without any complaints or errors.

To get a correct conversion I first have to assign the attribute to a string, replace the decimal '.' to a decimal ',' and then convert the string to a double. It is clearly that the Attribute["x"] can't convert but it doesn't say anything! (bug?!?)

Here is the code with faulty conversion:

double x = XMLNode->Attributes["x"];

This gives a faulty x of 25 instead of 2.5 and here is my work around:

String sd = XMLNode->Attributes["x"];
if (sd.Pos(".")) sd[sd.Pos(".")] = ',';
double x = sd.ToDouble();

This gives the correct value in x (2.5)

There MUST be a more simple way to do this!

// Thanks

Answer 1

XML attributes are arbitrary string values if you are not using an XSD to coherce the data, such as with the IDE's XML Data Binding wizard. The Attributes[] property returns an OleVariant, which in this case is going to contain a System::String in it. When a System::String is converted to a double using the OleVariant's double conversion operator or the String::ToDouble() method, the conversion uses the global SysUtils::DecimalSeparator variable, which is initialized using your PC's locale settings, which are clearly using the , character as a decimal separator instead of the . character. XML has no way of knowing that locale setting.

Since you are using a modern version of C++Builder, you can use the overloaded version of the StrToFloat() function that lets you pass in a TFormatSettings record as input. You can then specific . as the TFormatSettings::DecimalSeparator to use for the conversion, eg:

TFormatSettings fmt = TFormatSettings::Create();
fmt.DecimalSeparator = '.';
double x = StrToFloat(XMLNode->Attributes["x"], fmt);