If you code "mixed mode" assignment statements (i.e., assign a string to an integer, assign a single to a string, etc.), VB.NET will perform the necessary conversions in such statements whenever it possibly can (provided that "Option Strict" is off). Such conversions are called implicit conversions.
However, you can also use a set of functions that explicitly convert (or "cast") one type of data to another. The set of functions that enable you to do this all begin with the letter "C": CBool, CByte, CDate, CDbl, CDec, CInt, CLng, CSng, CStr, etc. Alternatively, you can use a corresponding method from the VB.NET Convert class to accomplish the same result.
In addition, two older functions, Val and Str, enable you to convert from a string to a number and from a number to a string, respectively.
The "Cxxx" functions and their equivalent Convert class methods are shown in the table below:
|
Function |
Convert Class Method |
Description |
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CBool |
Convert.ToBoolean |
Converts a numeric or string expression to Boolean. Numeric values of zero convert to False, all others to True. If the expression is String, it must be a string that can be converted to a number (like "123"). The strings "True" and "False" will also work; any other string will result in an error.
Examples:
blnTest = CBool(50) ' blnTest = True blnTest = CBool(0) ' blnTest = False blnTest = CBool("-26") ' blnTest = True blnTest = CBool("True") ' blnTest = True blnTest = CBool("False") ' blnTest = False blnTest = CBool("ABC") ' *** Error ***
blnTest = Convert.ToBoolean(50) ' blnTest = True blnTest = Convert.ToBoolean(0) ' blnTest = False blnTest = Convert.ToBoolean("-26") ' blnTest = True blnTest = Convert.ToBoolean("True") ' blnTest = True blnTest = Convert.ToBoolean("False")' blnTest = False blnTest = Convert.ToBoolean("ABC") ' *** Error ***
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CByte |
Convert.ToByte |
Converts a numeric expression in the range 0 to 255 to Byte. Fractional parts are rounded.
Examples:
bytX = CByte(125.5678) ' bytX = 126 bytX = CByte(300.99) ' error
bytX = Convert.ToByte(125.5678) ' bytX = 126 bytX = Convert.ToByte(300.99) ' error
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CChar |
Convert.ToChar |
Converts a Char or String expression to Char data type. If String, only first character is converted.
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CDate |
Convert.ToDate |
Converts a string expression containing a valid representation of a date/time to the Date (DateTime) data type. If the expression contains only a date portion, the resulting time component of the converted datetime value will be midnight. If the expression contains only a time portion, the resulting date component of the converted datetime value will be 1/1/0001.
Examples: dtmTest = CDate("1/18/2012") ' dtmTest = 1/18/2012 at midnight dtmTest = CDate("13:22") ' dtmTest = 1/1/0001 at 1:22 PM dtmTest = CDate("1/18/2021 1:22:00 PM") ' dtmTest = 1/18/2012 at 1:22 PM dtmTest = CDate("ABC") ' error
dtmTest = Convert.ToDate("1/18/2012") ' dtmTest = 1/18/2012 at midnight dtmTest = Convert.ToDate("13:22") ' dtmTest = 1/1/0001 at 1:22 PM dtmTest = Convert.ToDate("1/18/2021 1:22:00 PM") ' dtmTest = 1/18/2012 at 1:22 PM
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CDbl |
Convert.ToDouble |
Converts a numeric or string expression to Double. If string, must be string representation of a number. The value of the expression must be within the Double range.
Examples: dblTest = CDbl("1058.930") 'dblTest = 1058.93 dblTest = Convert.ToDouble("1058.930") 'dblTest = 1058.93
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CDec |
Convert.ToDecimal |
Converts a numeric or string expression to Decimal. If string, must be string representation of a number. The value of the expression must be within the Decimal range.
Examples: decTest = CDec("1058.930") 'decTest = 1058.93 decTest = Convert.ToDecimal("1058.930") 'decTest = 1058.93
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CInt |
Convert.ToInt32 |
Converts a numeric or string expression to Integer (Int32). If string, must be string representation of a number. The value of the expression must be within the Integer (Int32) range. Result is rounded.
Examples:
intX = CInt(-1.2) 'intX = -1 intX = CInt(-1.9) 'intX = -2 intX = CInt(3.69) 'intX = 4 intX = CInt(3.3) 'intX = 3
intX = Convert.ToInt32(-1.2) 'intX = -1 intX = Convert.ToInt32(-1.9) 'intX = -2 intX = Convert.ToInt32(3.69) 'intX = 4 intX = Convert.ToInt32(3.3) 'intX = 3
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CLng |
Convert.ToInt64 |
Converts a numeric or string expression to Long (Int64). If string, must be string representation of a number. The value of the expression must be within the Long (Int64) range. Result is rounded.
Examples:
lngX = CLng(-1.2) 'lngX = -1 lngX = CLng(-1.9) 'lngX = -2 lngX = CLng(3.69) 'lngX = 4 lngX = CLng(3.3) 'lngX = 3
lngX = Convert.ToLng64(-1.2) 'lngX = -1 lngX = Convert.ToLng64(-1.9) 'lngX = -2 lngX = Convert.ToLng64(3.69) 'lngX = 4 lngX = Convert.ToLng64 (3.3) 'lngX = 3
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CObj |
N/A |
Converts an expression of any type to an object. The object variable itself contains a four-byte pointer to expression assigned to it.
Example:
Dim intTest As Integer Dim objTest As Object ' the following line sets objTest to a pointer to intTest objTest = CObj(intTest)
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CSByte |
Convert.ToSByte |
Converts a numeric expression in the range -128 to 127 to Signed Byte. Fractional parts are rounded.
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CShort |
Convert.ToInt16 |
Converts a numeric or string expression to Short (Int16). If string, must be string representation of a number. The value of the expression must be within the Short (Int16) range. Result is rounded.
Examples:
intX = CShort(-1.2) 'intX = -1 intX = CShort(-1.9) 'intX = -2 intX = CShort(3.69) 'intX = 4 intX = CShort(3.3) 'intX = 3
intX = Convert.ToInt16(-1.2) 'intX = -1 intX = Convert.ToInt16(-1.9) 'intX = -2 intX = Convert.ToInt16(3.69) 'intX = 4 intX = Convert.ToInt16 (3.3) 'intX = 3
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CSng |
Convert.ToSingle |
Converts a numeric or string expression to Single. If string, must be string representation of a number. The value of the expression must be within the Single range.
Examples: sngTest = CSng("1058.930") 'sngTest = 1058.93 sngTest = Convert.ToSingle("1058.930") 'sngTest = 1058.93
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CStr |
Convert.ToString |
Converts a variable of any datatype to a string. If the argument is a Date, a "short date" string is returned. If the argument is Boolean, the string "True" or "False" is returned. If the argument is a number, a string representation of the number is returned.
Examples:
dtmTest1 = #1/18/2012# dtmTest2 = #1/18/2012 1:00 PM# blnTest = False sngTest = 123.456
strTest = CStr(dtmTest1) 'strTest = "1/18/2012" strTest = CStr(dtmTest2) 'strTest = "1/18/2012 1:00:00 PM" strTest = CStr(blnTest) 'strTest = "False" strTest = CStr(sngTest) 'strTest = "123.456"
strTest = Convert.ToString(dtmTest1) 'strTest = "1/18/2012" strTest = Convert.ToString(dtmTest2) 'strTest = "1/18/2012 1:00:00 PM" strTest = Convert.ToString(blnTest) 'strTest = "False" strTest = Convert.ToString(sngTest) 'strTest = "123.456"
NOTE: "ToString" is also a method that can be applied to any data type. So the following statements are also valid:
strTest = dtmTest1.ToString 'strTest = "1/18/2012" strTest = dtmTest2.ToString 'strTest = "1/18/2012 1:00:00 PM" strTest = blnTest.ToString 'strTest = "False" strTest = sngTest.ToString 'strTest = "123.456"
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CUInt |
Convert.ToUInt32 |
Converts a numeric or string expression to an unsigned integer (Int32). If string, must be string representation of a number. The value of the expression must be within the unsigned integer (Int32) range.
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CULng |
Convert.ToUInt64 |
Converts a numeric or string expression to an unsigned long integer (Int64). If string, must be string representation of a number. The value of the expression must be within the unsigned long integer (Int64) range.
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CUShort |
Convert.ToUInt16 |
Converts a numeric or string expression to an unsigned short integer (Int16). If string, must be string representation of a number. The value of the expression must be within the unsigned short integer (Int16) range.
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The CType Function
The CType function converts an expression to a specified data type. The syntax is:
variable = CType(expression, typename)
where expression is any valid expression that is within the range permitted by typename. Typename is any valid type that would be permitted within an As clause in a Dim statement, such as Integer, Date, String, etc.
Example:
Dim strNum As String = "1234.56"
Dim decNum As Decimal
decNum = CType(strNum, Decimal) ' decNum now contains 1234.56
The Val Function
The Val function is a generic way to convert a string to a number. Technically, it returns a Double data type. It strips all blanks from a string argument and then converts the remaining characters to a number. The Val function recognizes a leading sign, digits, and a decimal point as part of a number; it will stop scanning the string at the first character that cannot be considered part of a number. If the string cannot be converted to a number, 0 will be returned.
Examples: lngX = Val(" 1615 198th Street N.E.") 'lngX = 1615198intX =Val("2457")'intX = 2457
intX =Val(" 2 45 7")'intX = 2457
intX =Val("24 and 57")'intX = 24
sngX = Val("-1234.56") 'sngX = -1234.56 sngX = Val("-1,234.56") 'sngX = -1 dblX = Val("ABC") 'dblX = 0
Although less efficient than the "Cxxx" functions, one advantage to using Val is that if the string argument cannot be converted to a number, Val will simply return 0, whereas the equivalent "Cxxx" function would return a Type Mismatch error.
The Str Function
The Str function is an older function (dating back to earlier versions of BASIC) that converts a number to a string. When numbers are converted to strings, a leading space is always reserved for the sign of number. If number is positive, the returned string contains a leading space and the plus sign is implied. The Str function recognizes only the period (.) as a valid decimal separator.
Examples:
Dim strTest As String
strTest = Str(123) ' Returns " 123".
strTest = Str(-123.45) ' Returns "-123.45".
strTest = Str(789.001) ' Returns " 789.001".