CType, DirectCast, Parse, Convert fundamentals

[ashishraj14]

What is the fundamental difference between CType, DirectCast, Parse, Convert different?

thanks

 

[Dimandja]

The following example should illustrate the difference between CType and DirectCast.

Dim a As Object
Dim b As Object
Dim i As Integer

a = 1 [COLOR=green]'the object [b]a[/b] contains an integer[/color]
b = "1" [COLOR=green]'the object [b]b[/b] contains a string[/color]

i = DirectCast(a, Integer) [COLOR=green]'Good: a contains an integer[/color]

i = DirectCast(b, Integer) [COLOR=green]'Bad: b contains a string[/color]

i = CType(b, Integer) [COLOR=green]'Good: CType [b]will[/b] convert a string to an integer[/color]

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[ookete]

Yes, the Help files state: "DirectCast requires the run-time type of an object variable to be the same as the specified type". So the string "b" in the above example is not the same type as an integer, therefore failing the DirectCast.

 

[Dimandja]

Both CAST and CONVERT are used in Transact-SQL (MS SQL) to explicitly convert an expression of one data type to another. CAST and CONVERT provide similar functionality.

But, CAST offers other edit-like features. Check the following link for examples:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/tsqlref/ts_ca-co_2f3o.asp

PARSE, as in the DateTime.Parse Method, converts the specified string representation of a date and time to its DateTime equivalent.



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[SMURF75]

I add a little question

Difference between

Cstr(obj)
And
Ctype(obj ,String)

?

- - - - - - - - - - - - - - - - - -
Im three apples high, Im blue, and i most certainly like that cold beer that should be every mans right after a hard days work!

 

[ca8msm]

According to msdn:

CType is compiled inline, meaning the conversion code is part of the code that evaluates the expression. Execution is faster because there is no call to a procedure to accomplish the conversion.

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[Dimandja]

In addition to casting, CType will do a check for a valid destination data type; flagging Long to Integer, for example.

CInt, CStr and CBool will not check for valid data types.

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[ashishraj14]

thanks everyon3