String.Copy(String) 方法

參考

定義

命名空間:: System

組件:: System.Runtime.dll

組件:: mscorlib.dll

組件:: netstandard.dll

來源:: String.cs

來源:: String.cs

來源:: String.cs

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。

警告

This API should not be used to create mutable strings. See https://go.microsoft.com/fwlink/?linkid=2084035 for alternatives.

使用與指定的 String 相同的值，建立 String 的新執行個體。

public:
 static System::String ^ Copy(System::String ^ str);

[System.Obsolete("This API should not be used to create mutable strings. See https://go.microsoft.com/fwlink/?linkid=2084035 for alternatives.")]
public static string Copy (string str);

public static string Copy (string str);

[<System.Obsolete("This API should not be used to create mutable strings. See https://go.microsoft.com/fwlink/?linkid=2084035 for alternatives.")>]
static member Copy : string -> string

static member Copy : string -> string

Public Shared Function Copy (str As String) As String

參數

str: String

要複製的字串。

傳回

String

具有與 str 相同值的新字串。

屬性: ObsoleteAttribute

例外狀況

ArgumentNullException

str 為 null。

備註

方法 Copy 會傳 String 回與原始字串相同的值，但代表不同的物件參考。它與指派作業不同，它會將現有的字串參考指派給其他物件變數。

重要

從 .NET Core 3.0 開始，這個方法已過時。不過，我們不建議在任何 .NET 實作中使用。特別是，由於 .NET Core 3.0 中的字串插入變更，在某些情況下 Copy ，方法不會建立新的字串，而是只會傳回現有內嵌字串的參考。

根據您想要呼叫 Copy 方法的原因而定，有一些替代方法：

如果您想要在修改字串的作業中使用不同的字串實例，請使用原始字串實例。因為字串不可變，所以字串作業會建立新的字串實例，而原始字串仍不會受到影響。在此情況下，您不應該將新的字串參考指派給原始字串變數。下列範例提供說明。

var original = "This is a sentence. This is a second sentence.";
var sentence1 = original.Substring(0, original.IndexOf(".") + 1);
Console.WriteLine(original);
Console.WriteLine(sentence1);
// The example displays the following output:
//    This is a sentence. This is a second sentence.
//    This is a sentence.

let original = "This is a sentence. This is a second sentence."
let sentence1 = original.Substring(0, original.IndexOf "." + 1)
printfn $"{original}"
printfn $"{sentence1}"
// The example displays the following output:
//    This is a sentence. This is a second sentence.
//    This is a sentence.

Dim original = "This is a sentence. This is a second sentence."
Dim sentence1 = original.Substring(0, original.IndexOf(".") + 1)
Console.WriteLine(original)
Console.WriteLine(sentence1)
' The example displays the following output:
'    This is a sentence. This is a second sentence.
'    This is a sentence.

在此情況下，呼叫 Copy 方法以在呼叫方法之前 Substring 建立新的字串，不必要地建立新的字串實例。

如果您想要建立具有與原始字串相同內容的可變動緩衝區，請呼叫 String.ToCharArray 或 StringBuilder.StringBuilder(String) 建構函式。例如：

private static void UseMutableBuffer()
{
    var original = "This is a sentence. This is a second sentence.";
    var chars = original.ToCharArray();
    var span = new Span<char>(chars);
    var slice = span.Slice(span.IndexOf('.'), 3);
    slice = MergeSentence(slice);
    Console.WriteLine($"Original string: {original}");
    Console.WriteLine($"Modified string: {span.ToString()}");

    static Span<char> MergeSentence(Span<char> span)
    {
        if (span.Length == 0) return Span<char>.Empty;

        span[0] = ';';
        span[2] = Char.ToLower(span[2]);
        return span;
    }
}
// The example displays the following output:
//    Original string: This is a sentence. This is a second sentence.
//    Modified string: This is a sentence; this is a second sentence.

let mergeSentence (span: Span<char>) =
    if span.Length = 0 then
        Span<char>.Empty
    else
        span[0] <- '\000'
        span[2] <- Char.ToLower span[2]
        span

let useMutableBuffer () =
    let original = "This is a sentence. This is a second sentence."
    let chars = original.ToCharArray()
    let span = Span chars
    let slice = span.Slice(span.IndexOf '.', 3)
    let slice = mergeSentence slice
    let span = span.ToString()
    printfn $"Original string: {original}"
    printfn $"Modified string: {span}"
// The example displays the following output:
//    Original string: This is a sentence. This is a second sentence.
//    Modified string: This is a sentence this is a second sentence.

Private Sub UseMutableBuffer()
    Dim original = "This is a sentence. This is a second sentence."
    Dim sb = new StringBuilder(original)
    Dim index = original.IndexOf(".")
    sb(index) = ";"
    sb(index + 2) = Char.ToLower(sb(index + 2))
    Console.WriteLine($"Original string: {original}")
    Console.WriteLine($"Modified string: {sb.ToString()}")
End Sub
' The example displays the following output:
'    Original string: This is a sentence. This is a second sentence.
'    Modified string: This is a sentence; this is a second sentence.

如果您想要建立字串的可變動複本，以便使用不安全的程式碼來修改字串內容，請使用 Marshal.StringToHGlobalUni 方法。下列範例會 Marshal.StringToHGlobalUni 使用方法來取得非受控記憶體中複製字串位置的指標、將字串中每個字元的 Unicode 字碼點遞增一個，並將產生的字串複製到 Managed 字串。

private static void UseUnmanaged()
{
    var original = "This is a single sentence.";
    var len = original.Length; 
    var ptr = Marshal.StringToHGlobalUni(original);
    string? result;
    unsafe 
    {
        char *ch = (char *) ptr.ToPointer();
        while (len-- > 0)
        {
            char c = Convert.ToChar(Convert.ToUInt16(*ch) + 1);
            *ch++ = c;
        } 
        result = Marshal.PtrToStringUni(ptr);
        Marshal.FreeHGlobal(ptr);
    }
    Console.WriteLine($"Original string: {original}");
    Console.WriteLine($"String from interop: '{result}'");
}
// The example displays the following output:
//    Original string: This is a single sentence.
//    String from interop: 'Uijt!jt!b!tjohmf!tfoufodf/'

#nowarn "9"
open FSharp.NativeInterop

let useUnmanaged () =
    let original = "This is a single sentence."
    let mutable len = original.Length 
    let ptr = Marshal.StringToHGlobalUni original
    let mutable ch = ptr.ToPointer() |> NativePtr.ofVoidPtr<char> 
    while len > 0 do
        len <- len - 1
        Convert.ToUInt16(NativePtr.read ch) + 1us
        |> Convert.ToChar
        |> NativePtr.write (NativePtr.add ch 1)
        ch <- NativePtr.add ch 1

    let result = Marshal.PtrToStringUni ptr
    Marshal.FreeHGlobal ptr
    printfn $"Original string: {original}"
    printfn $"String from interop: '{result}'"

// The example displays the following output:
//    Original string: This is a single sentence.
//    String from interop: 'Uijt!jt!b!tjohmf!tfoufodf/'

適用於

共用方式為

String.Copy(String) 方法

定義

參數

傳回

例外狀況

備註

適用於

其他資源