This overload differs from the Double..::.Parse(String) method by returning a Boolean value that indicates whether the parse operation succeeded instead of returning the parsed numeric value. It eliminates the need to use exception handling to test for a FormatException in the event that s is invalid and cannot be successfully parsed.
Because of differences in precision, result may not be exactly equal to s, and for values of s that are less than Epsilon, result may also differ depending on processor architecture. For more information, see the Remarks section of Double.
The s parameter can contain the current culture's NumberFormatInfo..::.PositiveInfinitySymbol, NumberFormatInfo..::.NegativeInfinitySymbol, NumberFormatInfo..::.NaNSymbol (the string comparison is case-sensitive), or a string of the form:
[ws][sign][integral-digits,]integral-digits[.[fractional-digits]][e[sign]exponential-digits][ws]
Elements in square brackets are optional. The following table describes each element.
Element | Description |
|---|
ws
| A series of white-space characters. |
sign
| A negative sign or positive sign symbol. |
integral-digits
| A series of numeric characters ranging from 0 to 9 that specify the integral part of the number. Integral-digits can be absent if there are fractional-digits. |
,
| A culture-specific group separator symbol. |
.
| A culture-specific decimal point symbol. |
fractional-digits
| A series of numeric characters ranging from 0 to 9 that specify the fractional part of the number. |
E
| An uppercase or lowercase character 'e', that indicates exponential (scientific) notation. |
exponential-digits
| A series of numeric characters ranging from 0 to 9 that specify an exponent. |
For more information about numeric formats, see Formatting Overview.
The s parameter is interpreted using a combination of the NumberStyles..::.Float and NumberStyles..::.AllowThousands flags. This means that white space and thousands separators are allowed but currency symbols are not. To explicitly define the elements (such as currency symbols, thousands separators, and white space) that can be present in s, use the Double..::.TryParse(String, NumberStyles, IFormatProvider, Double%) method overload.
The s parameter is parsed using the formatting information in a NumberFormatInfo object that is initialized for the current system culture. For more information, see NumberFormatInfo..::.CurrentInfo. To parse a string using the formatting information of some other specified culture, use the Double..::.TryParse(String, NumberStyles, IFormatProvider, Double%) method overload.
Ordinarily, if you pass the Double..::.TryParse method a string that is created by calling the Double..::.ToString method, the original Double value is returned. However, because of a loss of precision, the values may not be equal. In addition, the parse operation fails and returns false if you attempt to parse the string representation of either MinValue or MaxValue, as the following example illustrates.
Dim value As String
Dim number As Double
value = Double.MinValue.ToString()
If Double.TryParse(value, number) Then
Console.WriteLine(number)
Else
Console.WriteLine("{0} is outside the range of a Double.", _
value)
End If
value = Double.MaxValue.ToString()
If Double.TryParse(value, number) Then
Console.WriteLine(number)
Else
Console.WriteLine("{0} is outside the range of a Double.", _
value)
End If
' The example displays the following output:
' -1.79769313486232E+308 is outside the range of the Double type.
' 1.79769313486232E+308 is outside the range of the Double type.
string value;
double number;
value = Double.MinValue.ToString();
if (Double.TryParse(value, out number))
Console.WriteLine(number);
else
Console.WriteLine("{0} is outside the range of a Double.",
value);
value = Double.MaxValue.ToString();
if (Double.TryParse(value, out number))
Console.WriteLine(number);
else
Console.WriteLine("{0} is outside the range of a Double.",
value);
// The example displays the following output:
// -1.79769313486232E+308 is outside the range of the Double type.
// 1.79769313486232E+308 is outside the range of the Double type.
If a separator is encountered in the s parameter during a parse operation, and the decimal and group separators are the same, the parse operation assumes that the separator is a decimal separator rather than a group separator. For more information about separators, see CurrencyDecimalSeparator, NumberDecimalSeparator, CurrencyGroupSeparator, and NumberGroupSeparator.