How can I use Convert.ChangeType to convert string into numerics with group separator?

Question

Hello,

I want to make a generic string to numeric converter, and provide it as a string extension, so I wrote the following code:

public static bool TryParse<T>( this string text, out T result, IFormatProvider formatProvider ) where T : struct
try
{
   result = (T)Convert.ChangeType( text, typeof( T ), formatProvider );
   return true;
}
catch(...

I call it like this:

int value;
var ok = "123".TryParse(out value, NumberFormatInfo.CurrentInfo)

It works fine until I want to use a group separator: As I live in France, where the thousand separator is a space and the decimal separator is a comma, the string "1 234 567,89" should be equals to 1234567.89 (in Invariant culture). But, the function crashes!

When a try to perform a non generic conversion, like double.Parse(...), I can use an overload which accepts a NumberStyles parameter. I specify NumberStyles.Number and this time it works!

So, the questions are :

• Why the parsing does not respect my NumberFormatInfo (where the NumberGroupSeparator is well specified to a space, as I specified in my OS)
• How could I make work the generic version with Convert.ChangeTime, as it has no overload wich accepts a NumberStyles parameter ?

Answer 1

Try specifying explicitly the culture "fr-FR":

CultureInfo c = new CultureInfo("fr-FR");
double d = 0;
if ("1 234 567,89".TryParse<double>(out d, c)) {
    Console.WriteLine(d);
}

EDIT: this example works properly:

static class Extension {
    public static bool TryParse<T>(this string text, out T result, IFormatProvider formatProvider) where T : struct {
        result = default(T);
        try {
            result = (T)Convert.ChangeType(text, typeof(T), formatProvider);
            return true;
        } catch {
            return false;
        }
    }

}

class Program {
    static void Main(string[] args) {
        CultureInfo c = new CultureInfo("fr-FR");
        double d = 0;
        // NumberGroupSeparator in fr-FR culture is space
        bool res = "123 456,78".TryParse<double>(out d, c);
        // Set separator as '.' and parse string with dots
        c.NumberFormat.NumberGroupSeparator = ".";
        res = "123.456,78".TryParse<double>(out d, c);
    }
}

Est-ce que ca marche comme ca? :)