Encoding::GetChars Method (array<Byte>, Int32, Int32, array<Char>, Int32)

When overridden in a derived class, decodes a sequence of bytes from the specified byte array into the specified character array.

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

public:
virtual int GetChars(
	array<unsigned char>^ bytes, 
	int byteIndex, 
	int byteCount, 
	array<wchar_t>^ chars, 
	int charIndex
) abstract

Parameters

bytes
Type: array<System::Byte>

The byte array containing the sequence of bytes to decode.

byteIndex
Type: System::Int32

The index of the first byte to decode.

byteCount
Type: System::Int32

The number of bytes to decode.

chars
Type: array<System::Char>

The character array to contain the resulting set of characters.

charIndex
Type: System::Int32

The index at which to start writing the resulting set of characters.

Return Value

Type: System::Int32
The actual number of characters written into chars.

ExceptionCondition
ArgumentNullException

bytes is nullptr.

-or-

chars is nullptr.

ArgumentOutOfRangeException

byteIndex or byteCount or charIndex is less than zero.

-or-

byteindex and byteCount do not denote a valid range in bytes.

-or-

charIndex is not a valid index in chars.

ArgumentException

chars does not have enough capacity from charIndex to the end of the array to accommodate the resulting characters.

DecoderFallbackException

A fallback occurred (see Character Encoding in the .NET Framework for complete explanation)

-and-

DecoderFallback is set to DecoderExceptionFallback.

To calculate the exact array size required by GetChars to store the resulting characters, the application should use GetCharCount. To calculate the maximum array size, the application should use GetMaxCharCount. The GetCharCount method generally allows allocation of less memory, while the GetMaxCharCount method generally executes faster.

Encoding::GetChars gets characters from an input byte sequence. Encoding::GetChars is different than Decoder::GetChars because Encoding expects discrete conversions, while Decoder is designed for multiple passes on a single input stream.

If the data to be converted is available only in sequential blocks (such as data read from a stream) or if the amount of data is so large that it needs to be divided into smaller blocks, the application should use the Decoder or the Encoder provided by the GetDecoder method or the GetEncoder method, respectively, of a derived class.

Note    This method is intended to operate on Unicode characters, not on arbitrary binary data, such as byte arrays. If your application needs to encode arbitrary binary data into text, it should use a protocol such as uuencode, which is implemented by methods such as Convert::ToBase64CharArray.

The GetCharCount method determines how many characters result in decoding a sequence of bytes, and the GetChars method performs the actual decoding. The Encoding::GetChars method expects discrete conversions, in contrast to the Decoder::GetChars method, which handles multiple passes on a single input stream.

Several versions of GetCharCount and GetChars are supported. The following are some programming considerations for use of these methods:

  • The application might need to decode multiple input bytes from a code page and process the bytes using multiple calls. In this case, your application probably needs to maintain state between calls, because byte sequences can be interrupted when processed in batches. (For example, part of an ISO-2022 shift sequence may end one GetChars call and continue at the beginning of the next GetChars call. Encoding::GetChars will call the fallback for those incomplete sequences, but Decoder will remember those sequences for the next call.)

  • If the application handles string outputs, the GetString method is recommended. Since this method must check string length and allocate a buffer, it is slightly slower, but the resulting String type is to be preferred.

  • The byte version of GetChars(Byte*, Int32, Char*, Int32) allows some fast techniques, particularly with multiple calls to large buffers. Bear in mind, however, that this method version is sometimes unsafe, since pointers are required.

  • If your application must convert a large amount of data, it should reuse the output buffer. In this case, the GetChars(array<Byte>, Int32, Int32, array<Char>, Int32) version that supports output character buffers is the best choice.

  • Consider using the Decoder::Convert method instead of GetCharCount. The conversion method converts as much data as possible and throws an exception if the output buffer is too small. For continuous decoding of a stream, this method is often the best choice.

The following example converts a string from one encoding to another.

using namespace System;
using namespace System::Text;

int main()
{
   String^ unicodeString = "This string contains the unicode character Pi (\u03a0)";

   // Create two different encodings.
   Encoding^ ascii = Encoding::ASCII;
   Encoding^ unicode = Encoding::Unicode;

   // Convert the string into a byte array. 
   array<Byte>^unicodeBytes = unicode->GetBytes( unicodeString );

   // Perform the conversion from one encoding to the other. 
   array<Byte>^asciiBytes = Encoding::Convert( unicode, ascii, unicodeBytes );

   // Convert the new Byte into[] a char and[] then into a string. 
   array<Char>^asciiChars = gcnew array<Char>(ascii->GetCharCount( asciiBytes, 0, asciiBytes->Length ));
   ascii->GetChars( asciiBytes, 0, asciiBytes->Length, asciiChars, 0 );
   String^ asciiString = gcnew String( asciiChars );

   // Display the strings created before and after the conversion.
   Console::WriteLine( "Original String*: {0}", unicodeString );
   Console::WriteLine( "Ascii converted String*: {0}", asciiString );
}
// The example displays the following output: 
//    Original string: This string contains the unicode character Pi (Π) 
//    Ascii converted string: This string contains the unicode character Pi (?)

The following example encodes a string into an array of bytes, and then decodes a range of the bytes into an array of characters.

using namespace System;
using namespace System::Text;
void PrintCountsAndChars( array<Byte>^bytes, int index, int count, 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, decode eight bytes starting at index 0, 
   // and print out the counts and the resulting bytes.
   Console::Write( "BE array with BE encoding : " );
   PrintCountsAndChars( barrBE, 0, 8, u32BE );
   Console::Write( "LE array with LE encoding : " );
   PrintCountsAndChars( barrLE, 0, 8, u32LE );
}

void PrintCountsAndChars( array<Byte>^bytes, int index, int count, Encoding^ enc )
{

   // Display the name of the encoding used.
   Console::Write( "{0,-25} :", enc );

   // Display the exact character count. 
   int iCC = enc->GetCharCount( bytes, index, count );
   Console::Write( " {0,-3}", iCC );

   // Display the maximum character count. 
   int iMCC = enc->GetMaxCharCount( count );
   Console::Write( " {0,-3} :", iMCC );

   // Decode the bytes and display the characters. 
   array<Char>^chars = enc->GetChars( bytes, index, count );

   // The following is an alternative way to decode the bytes: 
   // Char[] chars = new Char[iCC]; 
   // enc->GetChars( bytes, index, count, chars, 0 );
   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 : 2   6   :za
LE array with LE encoding : System.Text.UTF32Encoding : 2   6   :za

*/

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Was this page helpful?
(1500 characters remaining)
Thank you for your feedback
Show:
© 2014 Microsoft