字串範例
這個範例示範如何使用 Unmanaged 函式傳回的字串，以及如何傳遞含有 Unicode 格式或 ANSI 格式字串的結構。它顯示如何正確地初始化這些字串，以及如何擷取傳回值。
字串範例使用下列 Unmanaged 函式，顯示其原始函式宣告：
從 PinvokeLib.dll 匯出 TestStringAsResult。
char* TestStringAsResult();從 PinvokeLib.dll 匯出 TestStringInStruct。
void TestStringInStruct(MYSTRSTRUCT* pStruct);從 PinvokeLib.dll 匯出 TestStringInStructAnsi。
void TestStringInStructAnsi(MYSTRSTRUCT2* pStruct);
PinvokeLib.dll 是自訂的 Unmanaged 程式庫，包含先前列在函式和兩個結構 (MYSTRSTRUCT 與 MYSTRSTRUCT2) 的實作。這些結構包含下列元素：
typedef struct _MYSTRSTRUCT
{
wchar_t* buffer;
UINT size;
} MYSTRSTRUCT;
typedef struct _MYSTRSTRUCT2
{
char* buffer;
UINT size;
} MYSTRSTRUCT2;
在這個範例中，Managed MyStrStruct 和 MyStrStruct2 結構包含 Managed 字串而非 StringBuilder 緩衝區，因為 StringBuilder 型別無法在結構內使用。設定 StructLayoutAttribute 屬性以確保成員是以其出現的順序在記憶體中被循序配置。CharSet 欄位已設定為指定 ANSI 或 Unicode 格式。
LibWrap 類別包含 App 類別呼叫的 Managed 原型方法。雖然結構一般是以傳值 (By Value) 方式傳遞，但是 TestStringInStruct 和 TestStringInStructAnsi 方法的引數會以 ref (在 Visual Basic 中為 ByRef) 關鍵字標示，其以傳址 (By Reference) 方式傳遞結構。
下列程式碼範例的原始程式碼是由 .NET Framework 平台叫用技術範例所提供。
宣告原型
' Declares a managed structure for each unmanaged structure.
< StructLayout( LayoutKind.Sequential, CharSet:=CharSet.Unicode )> _
Public Structure MyStrStruct
Public buffer As String
Public size As Integer
End Structure 'MyStrStruct
< StructLayout( LayoutKind.Sequential, CharSet:=CharSet.Ansi )> _
Public Structure MyStrStruct2
Public buffer As String
Public size As Integer
End Structure 'MyStrStruct2
Public Class LibWrap
' Declares managed prototypes for unmanaged functions.
Declare Function TestStringAsResult Lib "..\LIB\PinvokeLib.dll" () _
As String
Declare Sub TestStringInStruct Lib "..\LIB\PinvokeLib.dll" _
( ByRef mss As MyStrStruct )
Declare Sub TestStringInStructAnsi Lib "..\LIB\PinvokeLib.dll" _
( ByRef mss As MyStrStruct2 )
End Class 'LibWrap
// Declares a managed structure for each unmanaged structure.
[ StructLayout( LayoutKind.Sequential, CharSet=CharSet.Unicode )]
public struct MyStrStruct
{
public String buffer;
public int size;
}
[ StructLayout( LayoutKind.Sequential, CharSet=CharSet.Ansi )]
public struct MyStrStruct2
{
public String buffer;
public int size;
}
public class LibWrap
{
// Declares managed prototypes for unmanaged functions.
[DllImport( "..\\LIB\\PinvokeLib.dll" )]
public static extern String TestStringAsResult();
[DllImport( "..\\LIB\\PinvokeLib.dll" )]
public static extern void TestStringInStruct( ref MyStrStruct mss );
[DllImport( "..\\LIB\\PinvokeLib.dll" )]
public static extern void TestStringInStructAnsi( ref MyStrStruct2
mss );
}
呼叫函式
Public Class App
Public Shared Sub Main()
' String as result.
Dim strng As String = LibWrap.TestStringAsResult()
Console.WriteLine( ControlChars.CrLf + "String returned: {0}", _
strng )
' Initializes buffer and appends something to the end so the whole
' buffer is passed to the unmanaged side.
Dim buffer As New StringBuilder( "content", 100 )
buffer.Append( ChrW(0) )
buffer.Append( "*"c, buffer.Capacity - 8)
Dim mss As MyStrStruct
mss.buffer = buffer.ToString()
mss.size = mss.buffer.Length
LibWrap.TestStringInStruct( mss )
Console.WriteLine( ControlChars.CrLf + _
"Buffer after Unicode function call: {0}", mss.buffer )
Dim buffer2 As New StringBuilder( "content", 100 )
buffer2.Append( ChrW(0) )
buffer2.Append( "*"c, buffer2.Capacity - 8 )
Dim mss2 As MyStrStruct2
mss2.buffer = buffer2.ToString()
mss2.size = mss2.buffer.Length
LibWrap.TestStringInStructAnsi( mss2 )
Console.WriteLine( ControlChars.CrLf + _
"Buffer after Ansi function call: {0}", mss2.buffer )
End Sub 'Main
End Class 'App
public class App
{
public static void Main()
{
// String as result.
String str = LibWrap.TestStringAsResult();
Console.WriteLine( "\nString returned: {0}", str );
// Initializes buffer and appends something to the end so the whole
// buffer is passed to the unmanaged side.
StringBuilder buffer = new StringBuilder( "content", 100 );
buffer.Append( (char)0 );
buffer.Append( '*', buffer.Capacity - 8 );
MyStrStruct mss;
mss.buffer = buffer.ToString();
mss.size = mss.buffer.Length;
LibWrap.TestStringInStruct( ref mss );
Console.WriteLine( "\nBuffer after Unicode function call: {0}",
mss.buffer );
StringBuilder buffer2 = new StringBuilder( "content", 100 );
buffer2.Append( (char)0 );
buffer2.Append( '*', buffer2.Capacity - 8 );
MyStrStruct2 mss2;
mss2.buffer = buffer2.ToString();
mss2.size = mss2.buffer.Length;
LibWrap.TestStringInStructAnsi( ref mss2 );
Console.WriteLine( "\nBuffer after Ansi function call: {0}",
mss2.buffer );
}
}