Decimal.Parse and Double.Parse System.FormatException Different behavior

Question

I do not understand why I have to specify NumberStyles.Float when using decimal.Parse and not for double.Parse

I can do:

var tmp = double.Parse("1e-2");

but not:

var tmp1 = decimal.Parse("1e-2"); 

Because a System.FormatException (Input string was not in a correct format) is thrown

var tmp1 = decimal.Parse("1e-2", System.Globalization.NumberStyles.Float);

someone can tell me if there is a good reason behind this behavior

Answer 1

It's just behaving as documented. From Double.Parse:

The s parameter is interpreted using a combination of the NumberStyles.Float and NumberStyles.AllowThousands flags.

Note that NumberStyles.Float includes NumberStyles.AllowExponent.

From Decimal.Parse:

Parameter s is interpreted using the NumberStyles.Number style.

NumberStyles.Number does not include NumberStyles.AllowExponent.

I can't reproduce your bizarre stack traces which appear to show the same call failing just after it's worked:

• Decimal.Parse("1e-2") always fails for me
• Decimal.Parse("1e-2", NumberStyles.Float) always works for me
• Double.Parse("1e-2") always works for me
• Double.Parse("1e-2", NumberStyles.Float) always works for me

As for why the "default" number style differs between the two - I suspect it's because double values typically are used in scientific scenarios where exponent-based representations are common, but decimal values typically aren't.