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VB.NET Language in a Nutshell, Second Edition by Steven Roman PhD, Paul Lomax, Ron Petrusha

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Name

CLng Function

Named Arguments

No

Syntax

CLng(expression)
expression (required; Numeric or String)

Ranges from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807; fractions are rounded.

Return Value

expression cast as a Long data type

Description

Converts expression to a long integer; any fractional element of expression is rounded.

Rules at a Glance

  • expression must evaluate to a numeric value; otherwise, a type-mismatch error is generated.

  • If the value of expression is outside the range of the Long data type, an overflow error is generated.

  • When the fractional part is exactly .5, CLng always rounds it to the nearest even number. For example, .5 rounds to 0, and 1.5 rounds to 2.

Example

Dim lngMyNumber as Long
If IsNumeric(sMyNumber) then
    lngMyNumber = CLng(sMyNumber)
End If

Programming Tips and Gotchas

  • When converting a string representation of a number to a numeric, you should use the data type conversion functions — such as CLng — instead of Val, because the data type conversion function takes into account the system’s regional settings. In particular, CLng is able to recognize the thousands separator if it’s included in expression, while Val cannot. For example, if a user enters a value of 1,098,234 into a textbox, CLng converts it to the long integer 1098234, but Val converts it to a value of 1.

  • Use IsNumeric to test whether expression evaluates to a number.

  • CLng differs from the Fix and Int functions, which truncate, rather than round, the fractional part of a number. Also, ...

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