Encoding.GetMaxCharCount(Int32) 方法
定義
重要
部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。
在衍生類別中覆寫時，計算解碼指定的位元組數目所產生的最大字元數目。
public:
abstract int GetMaxCharCount(int byteCount);public abstract int GetMaxCharCount (int byteCount);abstract member GetMaxCharCount : int -> intPublic MustOverride Function GetMaxCharCount (byteCount As Integer) As Integer參數
- byteCount
- Int32
要解碼的位元組數。
傳回
解碼指定位元組數所產生的最大字元數。
例外狀況
byteCount 小於零。
發生後援 (如需詳細資訊，請參閱 .NET 中的字元編碼)
-和-
範例
下列範例會將字元串編碼為位元組陣列，然後將位元組譯碼為字元陣列。
using namespace System;
using namespace System::Text;
void PrintCountsAndChars( array<Byte>^bytes, Encoding^ enc );
int main()
{
// Create two instances of UTF32Encoding: one with little-endian byte order and one with big-endian byte order.
Encoding^ u32LE = Encoding::GetEncoding( "utf-32" );
Encoding^ u32BE = Encoding::GetEncoding( "utf-32BE" );
// Use a string containing the following characters:
// Latin Small Letter Z (U+007A)
// Latin Small Letter A (U+0061)
// Combining Breve (U+0306)
// Latin Small Letter AE With Acute (U+01FD)
// Greek Small Letter Beta (U+03B2)
String^ myStr = "za\u0306\u01FD\u03B2";
// Encode the string using the big-endian byte order.
array<Byte>^barrBE = gcnew array<Byte>(u32BE->GetByteCount( myStr ));
u32BE->GetBytes( myStr, 0, myStr->Length, barrBE, 0 );
// Encode the string using the little-endian byte order.
array<Byte>^barrLE = gcnew array<Byte>(u32LE->GetByteCount( myStr ));
u32LE->GetBytes( myStr, 0, myStr->Length, barrLE, 0 );
// Get the char counts, and decode the byte arrays.
Console::Write( "BE array with BE encoding : " );
PrintCountsAndChars( barrBE, u32BE );
Console::Write( "LE array with LE encoding : " );
PrintCountsAndChars( barrLE, u32LE );
}
void PrintCountsAndChars( array<Byte>^bytes, Encoding^ enc )
{
// Display the name of the encoding used.
Console::Write( "{0,-25} :", enc );
// Display the exact character count.
int iCC = enc->GetCharCount( bytes );
Console::Write( " {0,-3}", iCC );
// Display the maximum character count.
int iMCC = enc->GetMaxCharCount( bytes->Length );
Console::Write( " {0,-3} :", iMCC );
// Decode the bytes and display the characters.
array<Char>^chars = enc->GetChars( bytes );
Console::WriteLine( chars );
}
/*
This code produces the following output. The question marks take the place of characters that cannot be displayed at the console.
BE array with BE encoding : System.Text.UTF32Encoding : 5 12 :zăǽβ
LE array with LE encoding : System.Text.UTF32Encoding : 5 12 :zăǽβ
*/
using System;
using System.Text;
public class SamplesEncoding {
public static void Main() {
// Create two instances of UTF32Encoding: one with little-endian byte order and one with big-endian byte order.
Encoding u32LE = Encoding.GetEncoding( "utf-32" );
Encoding u32BE = Encoding.GetEncoding( "utf-32BE" );
// Use a string containing the following characters:
// Latin Small Letter Z (U+007A)
// Latin Small Letter A (U+0061)
// Combining Breve (U+0306)
// Latin Small Letter AE With Acute (U+01FD)
// Greek Small Letter Beta (U+03B2)
String myStr = "za\u0306\u01FD\u03B2";
// Encode the string using the big-endian byte order.
byte[] barrBE = new byte[u32BE.GetByteCount( myStr )];
u32BE.GetBytes( myStr, 0, myStr.Length, barrBE, 0 );
// Encode the string using the little-endian byte order.
byte[] barrLE = new byte[u32LE.GetByteCount( myStr )];
u32LE.GetBytes( myStr, 0, myStr.Length, barrLE, 0 );
// Get the char counts, and decode the byte arrays.
Console.Write( "BE array with BE encoding : " );
PrintCountsAndChars( barrBE, u32BE );
Console.Write( "LE array with LE encoding : " );
PrintCountsAndChars( barrLE, u32LE );
}
public static void PrintCountsAndChars( byte[] bytes, Encoding enc ) {
// Display the name of the encoding used.
Console.Write( "{0,-25} :", enc.ToString() );
// Display the exact character count.
int iCC = enc.GetCharCount( bytes );
Console.Write( " {0,-3}", iCC );
// Display the maximum character count.
int iMCC = enc.GetMaxCharCount( bytes.Length );
Console.Write( " {0,-3} :", iMCC );
// Decode the bytes and display the characters.
char[] chars = enc.GetChars( bytes );
Console.WriteLine( chars );
}
}
/*
This code produces the following output. The question marks take the place of characters that cannot be displayed at the console.
BE array with BE encoding : System.Text.UTF32Encoding : 5 12 :zăǽβ
LE array with LE encoding : System.Text.UTF32Encoding : 5 12 :zăǽβ
*/
Imports System.Text
Public Class SamplesEncoding
Public Shared Sub Main()
' Create two instances of UTF32Encoding: one with little-endian byte order and one with big-endian byte order.
Dim u32LE As Encoding = Encoding.GetEncoding("utf-32")
Dim u32BE As Encoding = Encoding.GetEncoding("utf-32BE")
' Use a string containing the following characters:
' Latin Small Letter Z (U+007A)
' Latin Small Letter A (U+0061)
' Combining Breve (U+0306)
' Latin Small Letter AE With Acute (U+01FD)
' Greek Small Letter Beta (U+03B2)
Dim myStr As String = "za" & ChrW(&H0306) & ChrW(&H01FD) & ChrW(&H03B2)
' Encode the string using the big-endian byte order.
' NOTE: In VB.NET, arrays contain one extra element by default.
' The following line creates the array with the exact number of elements required.
Dim barrBE(u32BE.GetByteCount(myStr) - 1) As Byte
u32BE.GetBytes(myStr, 0, myStr.Length, barrBE, 0)
' Encode the string using the little-endian byte order.
' NOTE: In VB.NET, arrays contain one extra element by default.
' The following line creates the array with the exact number of elements required.
Dim barrLE(u32LE.GetByteCount(myStr) - 1) As Byte
u32LE.GetBytes(myStr, 0, myStr.Length, barrLE, 0)
' Get the char counts, and decode the byte arrays.
Console.Write("BE array with BE encoding : ")
PrintCountsAndChars(barrBE, u32BE)
Console.Write("LE array with LE encoding : ")
PrintCountsAndChars(barrLE, u32LE)
End Sub
Public Shared Sub PrintCountsAndChars(bytes() As Byte, enc As Encoding)
' Display the name of the encoding used.
Console.Write("{0,-25} :", enc.ToString())
' Display the exact character count.
Dim iCC As Integer = enc.GetCharCount(bytes)
Console.Write(" {0,-3}", iCC)
' Display the maximum character count.
Dim iMCC As Integer = enc.GetMaxCharCount(bytes.Length)
Console.Write(" {0,-3} :", iMCC)
' Decode the bytes and display the characters.
Dim chars As Char() = enc.GetChars(bytes)
Console.WriteLine(chars)
End Sub
End Class
'This code produces the following output. The question marks take the place of characters that cannot be displayed at the console.
'
'BE array with BE encoding : System.Text.UTF32Encoding : 5 12 :zăǽβ
'LE array with LE encoding : System.Text.UTF32Encoding : 5 12 :zăǽβ
備註
若要計算儲存所產生字元所需的 GetChars 確切數位大小，您應該使用 GetCharCount 方法。 若要計算數位大小上限，請使用 GetMaxCharCount 方法。 方法 GetCharCount 通常允許配置較少的記憶體，而 GetMaxCharCount 方法通常會執行得更快。
GetMaxCharCount 會擷取最差大小寫的數位，包括目前選取 DecoderFallback的最差大小寫。 如果選擇具有可能大型字串的後援， GetMaxCharCount 則會擷取大值。
在大部分情況下，此方法會擷取小型字串的合理數位。 對於大型字串，您可能必須在使用非常大的緩衝區和攔截錯誤之間做選擇，在罕見的情況下，較合理的緩衝區太小。 您也可以考慮使用 GetCharCount 或 Decoder.Convert的不同方法。
GetMaxCharCount 與沒有關聯 GetBytes。 如果您需要與 搭配 GetBytes使用的類似函式，您應該使用 GetMaxByteCount。
使用 GetMaxCharCount時，您應該根據輸入緩衝區的大小上限來配置輸出緩衝區。 如果輸出緩衝區的大小受限，您可以使用 Decoder.Convert 方法。
請注意， GetMaxCharCount 會考慮先前編碼器作業中剩餘位元組的最差情況。 對於大部分的代碼頁，將值 0 傳遞至這個方法會擷取大於或等於 1 的值。
注意
GetMaxCharCount(N) 不一定與 相同的值 N* GetMaxCharCount(1)。
給實施者的注意事項
所有 Encoding 實作都必須保證，如果緩衝區根據此方法計算的結果重設大小，則不會發生任何緩衝區溢位例外狀況。
