System 命名空間


.NET Framework 類別庫
Convert 類別

更新：2007 年 11 月

將基底資料型別轉換為其他基底資料型別。

命名空間：  System
組件：  mscorlib (在 mscorlib.dll 中)
語法
Visual Basic (宣告) 
Public NotInheritable Class Convert
Visual Basic (使用方式) 
您不需宣告靜態類別的執行個體，就能存取其成員。
C# 
public static class Convert
Visual C++ 
public ref class Convert abstract sealed
J# 
public final class Convert
JScript 
public final class Convert
備註

這個類別傳回和指定型別之值相等的型別。支援的基底型別 (Base Type) 有 Boolean、Char、SByte、Byte、Int16、Int32、Int64、UInt16、UInt32、UInt64、Single、Double、Decimal、DateTime 和 String。

轉換方法可用來轉換每個基底型別為其他的基底型別。然而，實際呼叫某個特定的轉換方法，可能會產生四種結果，視執行階段的基底型別值及目標基底型別而有所不同。這四種結果是：

  • 無轉換。嘗試從某個型別轉換到本身 (例如，以型別為 Int32 的引數呼叫 Convert..::.ToInt32(Int32))，就會發生這種情形。在這種情況下，這個方法只會傳回原始型別的執行個體。

  • InvalidCastException。如果不支援某個特定轉換，就會發生這種情形。執行下列轉換，就會擲回 InvalidCastException：

  • 轉換成功。至於先前結果中未列出的兩個不同基底型別之間的轉換，只要不會產生資料遺失，所有擴展轉換以及所有縮小轉換都可以成功，此方法也會傳回目標基底型別的值。

  • OverflowException。如果縮小轉換導致資料遺失，就會發生這種情形。例如，嘗試將值為 10000 的 Int32 執行個體轉換到 Byte 型別，就會擲回 OverflowException，因為 10000 已超出 Byte 資料型別的範圍。

如果數字型別 (Numeric Type) 的轉換導致精確度的遺失 (也就是說，遺失部分最小有效位數)，將不會擲回例外狀況。然而，如果結果大於特定轉換方法的傳回值型別可以表示的值，將擲回例外狀況。

例如，在將 Double 轉換為 Single 時，可能會發生精確度的遺失，但是不會擲回例外狀況。然而，如果 Double 的範圍超過 Single 可以表示的範圍，將擲回溢位例外狀況。

一組方法會支援轉換位元組陣列及 String，或由 Base 64 位數字元所組成的 Unicode 字元陣列之間的轉換。以 Base 64 位數表示的資料可以很容易地在只能傳輸 7 位元字元的資料通道上傳遞。

這個類別中的部分方法採用實作 IFormatProvider 介面的參數物件。這個參數可以提供特定文化特性的格式資訊，協助轉換處理。基底實值型別會忽略這個參數，但任何實作 IConvertible 的使用者定義型別可以承認它。

如需基底值型別的詳細資訊，請參閱「請參閱」章節中所列示的相關主題。

範例

下列程式碼範例示範 Convert 類別 (Class) 中的部分轉換方法，包含 ToInt32、ToBoolean 和 ToString。

Visual Basic 
Dim dNumber As Double
dNumber = 23.15

Try
   ' Returns 23
   Dim iNumber As Integer
   iNumber = System.Convert.ToInt32(dNumber)
Catch exp As System.OverflowException
   System.Console.WriteLine("Overflow in double to int conversion.")
End Try

' Returns True
Dim bNumber As Boolean
bNumber = System.Convert.ToBoolean(dNumber)

' Returns "23.15"
Dim strNumber As String
strNumber = System.Convert.ToString(dNumber)

Try
   ' Returns '2'
   Dim chrNumber As Char
   chrNumber = System.Convert.ToChar(strNumber.Chars(1))
Catch exp As System.ArgumentNullException
   System.Console.WriteLine("String is null.")
Catch exp As System.FormatException
   System.Console.WriteLine("String length is greater than 1.")
End Try

' System.Console.ReadLine() returns a string and it
' must be converted.
Dim newInteger As Integer
newInteger = 0
Try
   System.Console.WriteLine("Enter an integer:")
   newInteger = System.Convert.ToInt32(System.Console.ReadLine())
Catch exp As System.ArgumentNullException
   System.Console.WriteLine("String is null.")
Catch exp As System.FormatException
   System.Console.WriteLine("String does not consist of an " + _
       "optional sign followed by a series of digits.")
Catch exp As System.OverflowException
   System.Console.WriteLine("Overflow in string to int conversion.")
End Try

System.Console.WriteLine("Your integer as a double is {0}", _
                         System.Convert.ToDouble(newInteger))
C# 
            double dNumber = 23.15;

            try {
                // Returns 23
                int    iNumber = System.Convert.ToInt32(dNumber);
            }
            catch (System.OverflowException) {
                System.Console.WriteLine(
                            "Overflow in double to int conversion.");
            }
            // Returns True
            bool   bNumber = System.Convert.ToBoolean(dNumber);
            
            // Returns "23.15"
            string strNumber = System.Convert.ToString(dNumber);

            try {
                // Returns '2'
                char chrNumber = System.Convert.ToChar(strNumber[0]);
            } 
            catch (System.ArgumentNullException) {
                System.Console.WriteLine("String is null");
            }
            catch (System.FormatException) {
                System.Console.WriteLine("String length is greater than 1.");
            }

            // System.Console.ReadLine() returns a string and it
            // must be converted.
            int newInteger = 0;
            try {
                System.Console.WriteLine("Enter an integer:");
                newInteger = System.Convert.ToInt32(
                                    System.Console.ReadLine());
            }
            catch (System.ArgumentNullException) {
                System.Console.WriteLine("String is null.");
            }
            catch (System.FormatException) {
                System.Console.WriteLine("String does not consist of an " +
                                "optional sign followed by a series of digits.");
            } 
            catch (System.OverflowException) {
                System.Console.WriteLine(
                "Overflow in string to int conversion.");
            }

            System.Console.WriteLine("Your integer as a double is {0}",
                                     System.Convert.ToDouble(newInteger));
Visual C++ 
Double dNumber = 23.15;

try
{
   // Returns 23
   Int32 iNumber = Convert::ToInt32( dNumber );
}
catch ( OverflowException^ ) 
{
   Console::WriteLine(
      "Overflow in Double to Int32 conversion" );
}
// Returns True
Boolean bNumber = Convert::ToBoolean( dNumber );

// Returns "23.15"
String^ strNumber = Convert::ToString( dNumber );

try
{
   // Returns '2'
   Char chrNumber = Convert::ToChar( strNumber->Substring( 0, 1 ) );
}
catch ( ArgumentNullException^ ) 
{
   Console::WriteLine(  "String is null" );
}
catch ( FormatException^ ) 
{
   Console::WriteLine(  "String length is greater than 1" );
}

// System::Console::ReadLine() returns a string and it
// must be converted.
Int32 newInteger = 0;
try
{
   Console::WriteLine(  "Enter an integer:" );
   newInteger = Convert::ToInt32( System::Console::ReadLine() );
}
catch ( ArgumentNullException^ ) 
{
   Console::WriteLine(  "String is null" );
}
catch ( FormatException^ ) 
{
   Console::WriteLine(  "String does not consist of an " +
      "optional sign followed by a series of digits" );
}
catch ( OverflowException^ ) 
{
   Console::WriteLine(  "Overflow in string to Int32 conversion" );
}

Console::WriteLine( "Your integer as a Double is {0}",
   Convert::ToDouble( newInteger ) );
J# 
double dNumber = 23.15;

try {        
    // Returns 23
    int iNumber = System.Convert.ToInt32(dNumber);
}
catch (System.OverflowException exp) {        
    System.Console.WriteLine("Overflow in double to int conversion.");
}

// Returns True
boolean bNumber = System.Convert.ToBoolean(dNumber);

// Returns "23.15"
String strNumber = System.Convert.ToString(dNumber);

try {        
    // Returns '2'
    char chrNumber = System.Convert.ToChar(strNumber.get_Chars(0));
}
catch (System.ArgumentNullException exp) {        
    System.Console.WriteLine("String is null");
}
catch (System.FormatException exp) {        
    System.Console.WriteLine("String length is greater than 1.");
}

// System.Console.ReadLine() returns a string and it
// must be converted.
int newInteger = 0;

try {        
    System.Console.WriteLine("Enter an integer:");
    newInteger = System.Convert.ToInt32(System.Console.ReadLine());
}
catch (System.ArgumentNullException exp) {        
    System.Console.WriteLine("String is null.");
}
catch (System.FormatException exp) {        
    System.Console.WriteLine(("String does not consist of an " 
        + "optional sign followed by a series of digits."));
}
catch (System.OverflowException exp) {        
    System.Console.WriteLine("Overflow in string to int conversion.");
}
System.Console.WriteLine("Your integer as a double is {0}", 
    System.Convert.ToString(System.Convert.ToDouble(newInteger)));

下列程式碼範例示範 Convert 類別 (Class) 中的數個轉換方法。

Visual Basic 
' Sample for the Convert class summary.
Imports System

Class Sample
   Public Shared Sub Main()
      Dim nl As String = Environment.NewLine
      Dim str As String = "{0}Return the Int64 equivalent of the following base types:{0}"
      Dim xBool As Boolean = False
      Dim xShort As Short = 1
      Dim xInt As Integer = 2
      Dim xLong As Long = 3
      Dim xSingle As Single = 4F
      Dim xDouble As Double = 5.0
      Dim xDecimal As Decimal = 6D
      Dim xString As String = "7"
      Dim xChar As Char = "8"c ' '8' = hexadecimal 38 = decimal 56
      Dim xByte As Byte = 9

      '  The following types are not CLS-compliant.
      ' Dim xUshort As System.UInt16 = 120
      ' Dim xUint As System.UInt32 = 121
      ' Dim xUlong As System.UInt64 = 122
      ' Dim xSbyte As System.SByte = 123

      '  The following type cannot be converted to an Int64.
      '  Dim xDateTime As System.DateTime = DateTime.Now

      Console.WriteLine(str, nl)
      Console.WriteLine("Boolean:  {0}", Convert.ToInt64(xBool))
      Console.WriteLine("Int16:    {0}", Convert.ToInt64(xShort))
      Console.WriteLine("Int32:    {0}", Convert.ToInt64(xInt))
      Console.WriteLine("Int64:    {0}", Convert.ToInt64(xLong))
      Console.WriteLine("Single:   {0}", Convert.ToInt64(xSingle))
      Console.WriteLine("Double:   {0}", Convert.ToInt64(xDouble))
      Console.WriteLine("Decimal:  {0}", Convert.ToInt64(xDecimal))
      Console.WriteLine("String:   {0}", Convert.ToInt64(xString))
      Console.WriteLine("Char:     {0}", Convert.ToInt64(xChar))
      Console.WriteLine("Byte:     {0}", Convert.ToInt64(xByte))
      Console.WriteLine("DateTime: There is no example of this conversion because")
      Console.WriteLine("          a DateTime cannot be converted to an Int64.")
      '
      Console.Write("{0}The following types are not supported: ", nl)
      Console.WriteLine("UInt16, UInt32, UInt64, and SByte")
   End Sub 'Main
End Class 'Sample
'
'This example produces the following results:
'
'Return the Int64 equivalent of the following base types:
'
'Boolean:  0
'Int16:    1
'Int32:    2
'Int64:    3
'Single:   4
'Double:   5
'Decimal:  6
'String:   7
'Char:     56
'Byte:     9
'DateTime: There is no example of this conversion because
'          a DateTime cannot be converted to an Int64.
'
'The following types are not supported: UInt16, UInt32, UInt64, and SByte
'
C# 
// Sample for the Convert class summary.
using System;

class Sample 
{
    public static void Main() 
    {
    string nl = Environment.NewLine;
    string str = "{0}Return the Int64 equivalent of the following base types:{0}";
    bool    xBool = false;
    short   xShort = 1;
    int     xInt   = 2;
    long    xLong  = 3;
    float   xSingle = 4.0f;
    double  xDouble = 5.0;
    decimal xDecimal = 6.0m;
    string  xString = "7";
    char    xChar   = '8'; // '8' = hexadecimal 38 = decimal 56
    byte    xByte  =  9;

//  The following types are not CLS-compliant.
    ushort  xUshort = 120;   
    uint    xUint =   121;
    ulong   xUlong =  122;
    sbyte   xSbyte  = 123;

//  The following type cannot be converted to an Int64.
//  DateTime xDateTime = DateTime.Now;

    Console.WriteLine(str, nl);
    Console.WriteLine("Boolean:  {0}", Convert.ToInt64(xBool));
    Console.WriteLine("Int16:    {0}", Convert.ToInt64(xShort));
    Console.WriteLine("Int32:    {0}", Convert.ToInt64(xInt));
    Console.WriteLine("Int64:    {0}", Convert.ToInt64(xLong));
    Console.WriteLine("Single:   {0}", Convert.ToInt64(xSingle));
    Console.WriteLine("Double:   {0}", Convert.ToInt64(xDouble));
    Console.WriteLine("Decimal:  {0}", Convert.ToInt64(xDecimal));
    Console.WriteLine("String:   {0}", Convert.ToInt64(xString));
    Console.WriteLine("Char:     {0}", Convert.ToInt64(xChar));
    Console.WriteLine("Byte:     {0}", Convert.ToInt64(xByte));
    Console.WriteLine("DateTime: There is no example of this conversion because");
    Console.WriteLine("          a DateTime cannot be converted to an Int64.");
//
    Console.WriteLine("{0}The following types are not CLS-compliant.{0}", nl);
    Console.WriteLine("UInt16:   {0}", Convert.ToInt64(xUshort));
    Console.WriteLine("UInt32:   {0}", Convert.ToInt64(xUint));
    Console.WriteLine("UInt64:   {0}", Convert.ToInt64(xUlong));
    Console.WriteLine("SByte:    {0}", Convert.ToInt64(xSbyte));
    }
}
/*
This example produces the following results:

Return the Int64 equivalent of the following base types:

Boolean:  0
Int16:    1
Int32:    2
Int64:    3
Single:   4
Double:   5
Decimal:  6
String:   7
Char:     56
Byte:     9
DateTime: There is no example of this conversion because
          a DateTime cannot be converted to an Int64.

The following types are not CLS-compliant.

UInt16:   120
UInt32:   121
UInt64:   122
SByte:    123
*/
Visual C++ 
// Sample for the Convert class summary.
using namespace System;
int main()
{
   String^ nl = Environment::NewLine;
   String^ str = " {0}Return the Int64 equivalent of the following base types: {0}";
   bool xBool = false;
   short xShort = 1;
   int xInt = 2;
   long xLong = 3;
   float xSingle = 4.0f;
   double xDouble = 5.0;
   Decimal xDecimal = Decimal(6.0);
   String^ xString = "7";
   char xChar = '8'; // '8' = hexadecimal 38 = decimal 56

   Byte xByte = 9;

   //  The following types are not CLS-compliant.
   UInt16 xUshort = 120;
   UInt32 xUint = 121;
   UInt64 xUlong = 122;
   SByte xSbyte = 123;

   //  The following type cannot be converted to an Int64.
   //  DateTime xDateTime = DateTime::Now;
   Console::WriteLine( str, nl );
   Console::WriteLine( "Boolean: {0}", Convert::ToInt64( xBool ) );
   Console::WriteLine( "Int16: {0}", Convert::ToInt64( xShort ) );
   Console::WriteLine( "Int32: {0}", Convert::ToInt64( xInt ) );
   Console::WriteLine( "Int64: {0}", Convert::ToInt64( xLong ) );
   Console::WriteLine( "Single: {0}", Convert::ToInt64( xSingle ) );
   Console::WriteLine( "Double: {0}", Convert::ToInt64( xDouble ) );
   Console::WriteLine( "Decimal: {0}", Convert::ToInt64( xDecimal ) );
   Console::WriteLine( "String: {0}", Convert::ToInt64( xString ) );
   Console::WriteLine( "Char: {0}", Convert::ToInt64( xChar ) );
   Console::WriteLine( "Byte: {0}", Convert::ToInt64( xByte ) );
   Console::WriteLine( "DateTime: There is no example of this conversion because" );
   Console::WriteLine( "          a DateTime cannot be converted to an Int64." );

   //
   Console::WriteLine( " {0}The following types are not CLS-compliant. {0}", nl );
   Console::WriteLine( "UInt16: {0}", Convert::ToInt64( xUshort ) );
   Console::WriteLine( "UInt32: {0}", Convert::ToInt64( xUint ) );
   Console::WriteLine( "UInt64: {0}", Convert::ToInt64( xUlong ) );
   Console::WriteLine( "SByte: {0}", Convert::ToInt64( xSbyte ) );
}

/*
This example produces the following results:

Return the Int64 equivalent of the following base types:

Boolean:  0
Int16:    1
Int32:    2
Int64:    3
Single:   4
Double:   5
Decimal:  6
String:   7
Char:     56
Byte:     9
DateTime: There is no example of this conversion because
a DateTime cannot be converted to an Int64.

The following types are not CLS-compliant.

UInt16:   120
UInt32:   121
UInt64:   122
SByte:    123
*/
繼承階層架構
System..::.Object
  System..::.Convert
執行緒安全
這個型別的任何 Public static (在 Visual Basic 中為 Shared) 成員都具備執行緒安全。並非所有的執行個體成員都是安全執行緒。
平台

Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360

.NET Framework 和 .NET Compact Framework 並不支援各種平台的所有版本。如需支援平台版本的相關資訊，請參閱 .NET Framework 系統需求。
版本資訊

.NET Framework

支援版本：3.5、3.0、2.0、1.1、1.0

.NET Compact Framework

支援版本：3.5、2.0、1.0

XNA Framework

支援版本：2.0、1.0
請參閱

參考

Convert 成員
System 命名空間
Object
SByte
Int16
Int32
Int64
Byte
UInt16
UInt32
UInt64
Single
Double
Decimal
Boolean
Char
String
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