Artikel
11/18/2011

Single.TryParse Method (String, Single%)

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Converts the string representation of a number to its single-precision floating-point number equivalent. A return code indicates whether the conversion succeeded or failed.

Namespace: System
Assembly: mscorlib (in mscorlib.dll)

Syntax

'Declaration
Public Shared Function TryParse ( _
    s As String, _
    <OutAttribute> ByRef result As Single _
) As Boolean

public static bool TryParse(
    string s,
    out float result
)

Parameters

s
Type: System.String
A string representing a number to convert.

result
Type: System.Single%
When this method returns, contains single-precision floating-point number equivalent to the numeric value or symbol contained in s, if the conversion succeeded, or zero if the conversion failed. The conversion fails if the s parameter is nulla null reference (Nothing in Visual Basic), is not a number in a valid format, or represents a number less than MinValue or greater than MaxValue. This parameter is passed uninitialized.

Return Value

Type: System.Boolean
true if s was converted successfully; otherwise, false.

Remarks

This overload differs from the Single.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.

The s parameter can contain PositiveInfinitySymbol, NegativeInfinitySymbol, 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.

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 TryParse(String, NumberStyles, IFormatProvider, Single%) 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 TryParse(String, NumberStyles, IFormatProvider, Single%) method overload.

Ordinarily, if you pass the Single.TryParse method a string that is created by calling the Single.ToString method, the original Single value is returned. However, because of a loss of precision, the values may not be equal.

If a separator is encountered in the s parameter during a parse operation, and the applicable currency or number 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.

Examples

The following example uses the TryParse(String, Single%) method to convert the string representations of numeric values to Single values. It assumes that en-US is the current culture.

Dim value As String
Dim number As Single

' Parse a floating-point value with a thousands separator.
value = "1,643.57"
If Single.TryParse(value, number) Then
   outputBlock.Text &= number & vbCrLf
Else
   outputBlock.Text += String.Format("Unable to parse '{0}'.", value) & vbCrLf
End If

' Parse a floating-point value with a currency symbol and a 
' thousands separator.
value = "$1,643.57"
If Single.TryParse(value, number) Then
   outputBlock.Text &= number & vbCrLf
Else
   outputBlock.Text += String.Format("Unable to parse '{0}'.", value) & vbCrLf
End If

' Parse value in exponential notation.
value = "-1.643e6"
If Single.TryParse(value, number) Then
   outputBlock.Text &= number & vbCrLf
Else
   outputBlock.Text += String.Format("Unable to parse '{0}'.", value) & vbCrLf
End If

' Parse a negative integer number.
value = "-168934617882109132"
If Single.TryParse(value, number) Then
   outputBlock.Text &= number & vbCrLf
Else
   outputBlock.Text += String.Format("Unable to parse '{0}'.", value) & vbCrLf
End If
' The example displays the following output:
'       1643.57
'       Unable to parse '$1,643.57'.
'       -1643000
'       -1.68934617882109E+17

string value;
float number;

// Parse a floating-point value with a thousands separator.
value = "1,643.57";
if (Single.TryParse(value, out number))
   outputBlock.Text += number + "\n";
else
   outputBlock.Text += String.Format("Unable to parse '{0}'.", value) + "\n";

// Parse a floating-point value with a currency symbol and a 
// thousands separator.
value = "$1,643.57";
if (Single.TryParse(value, out number))
   outputBlock.Text += number + "\n";
else
   outputBlock.Text += String.Format("Unable to parse '{0}'.", value) + "\n";

// Parse value in exponential notation.
value = "-1.643e6";
if (Single.TryParse(value, out number))
   outputBlock.Text += number + "\n";
else
   outputBlock.Text += String.Format("Unable to parse '{0}'.", value) + "\n";

// Parse a negative integer value.
value = "-168934617882109132";
if (Single.TryParse(value, out number))
   outputBlock.Text += number + "\n";
else
   outputBlock.Text += String.Format("Unable to parse '{0}'.", value) + "\n";
// The example displays the following output:
//       1643.57
//       Unable to parse '$1,643.57'.
//       -164300
//       -1.68934617882109E+17

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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