Derive Object Type from Format String

Question

Is it possible to derive the intended object type from a .NET format string in C#? For example:

//Input parameters
var formatString = "dd/MM/yyyy";  //or "£0.00" for example
var stringValue = "2014-04-01"; //or "37.34" for example

//Logic
object value = null;

if (IsADate(formatString)) {
    objectValue = DateTime.Parse(stringValue);

} else if (IsANumber(formatString)) {
    objectValue = double.Parse(stringValue);

} else //etc

//Result
var resultString = String.Format(value,formatString);

I could obviously write out the IsADate() and IsANumber() functions, but wondered whether there is anything in the Framework that covers this already?

Do you just want to parse the stringValue or do you really need a function that maps a formatString to a Type? — Dirk
– Dirk, Commented Jul 17, 2014 at 9:27

Perfect28 · Accepted Answer · 2014-07-17 09:36:19Z

3

DateTime.TryParseExact() will make you your IsDate() function and Int32.TryParse() will make you your IsNumber() function.

Finally you should have something like that :

DateTime dateTime ; 
int anInt;

if (DateTime.TryParseExact(formatString, stringValue , out dateTime)) {
    objectValue = DateTime.Parse(stringValue);

} else if (Int32.TryParse(stringValue , out anInt)) {
    objectValue = double.Parse(stringValue);

} else //etc

edited Jul 17, 2014 at 9:36

answered Jul 17, 2014 at 9:17

Perfect28

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5 Comments

MarkO Over a year ago

TryParse already outputs the DateTime if it succeeds, no need to Parse it a second time. objectValue = dateTime should be sufficient.

Thorsten Dittmar Over a year ago

What I don't understand about your answer: You are trying to convert dd/MM/yyyy into a DateTime? That won't work! You can not parse the format string. I guess what you want is TryParseExact(formatString, inputValue, out dateTime), which uses the format string to parse the given input into an ouput. If that works, chances are the format string was for a DateTime/int etc. And why do you double.Parse if you check whether it is an Int32?

Dirk Over a year ago

You should use DateTime.TryParseExact with the given formatString and stringValue and for ints your answer won't work.

Perfect28 Over a year ago

@Dirk : Thanks for your corretion.

Thorsten Dittmar Over a year ago

@Ksv3n How will Int32.TryParse("d", out anInt); ever return true? d is a valid numeric format string, but fails to be parsed as a numeric value.

Thorsten Dittmar · Accepted Answer · 2014-07-17 09:32:52Z

0

You could force .NET to try and parse your input given the format string where possible. If that succeeds, chances are good you got the right type:

var formatString = "dd/MM/yyyy";  //or "£0.00" for example
var stringValue = "2014-04-01"; //or "37.34" for example

//Logic
object value = null;
DateTime dtDummy;
int intDummy;

if (DateTime.TryParseExact(formatString, stringValue, out dtDummy)) {
    value = dtDummy;

} 
else
...

For some types (numeric types, for example) there's no such method.

edited Jul 17, 2014 at 9:32

answered Jul 17, 2014 at 9:27

Thorsten Dittmar

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2 Comments

Dirk Over a year ago

Numbers (int, double, etc.) don't have a static method accepting a format string for parsing.

Thorsten Dittmar Over a year ago

True. Then it's not possible to do that for numeric types, really.

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