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 屬性以確保成員是按照出現的順序，循序配置於記憶體中。 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。
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
<StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Ansi)> _
Public Structure MyStrStruct2
Public buffer As String
Public size As Integer
End Structure
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
// 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);
}
// Declares a managed structure for each unmanaged structure.
[StructLayout(LayoutKind::Sequential, CharSet=CharSet::Unicode)]
public value struct MyStrStruct
{
public:
String^ buffer;
int size;
};
[StructLayout(LayoutKind::Sequential, CharSet=CharSet::Ansi)]
public value struct MyStrStruct2
{
public:
String^ buffer;
int size;
};
public ref class LibWrap
{
public:
// Declares managed prototypes for unmanaged functions.
[DllImport("..\\LIB\\PinvokeLib.dll")]
static String^ TestStringAsResult();
[DllImport("..\\LIB\\PinvokeLib.dll")]
static void TestStringInStruct(MyStrStruct% mss);
[DllImport("..\\LIB\\PinvokeLib.dll")]
static void TestStringInStructAnsi(MyStrStruct2% mss);
};
呼叫函式
Public Class App
Public Shared Sub Main()
' String as result.
Dim str As String = LibWrap.TestStringAsResult()
Console.WriteLine(vbNewLine + "String returned: {0}", str)
' 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("*", buffer.Capacity - 8)
Dim mss As MyStrStruct
mss.buffer = buffer.ToString()
mss.size = mss.buffer.Length
LibWrap.TestStringInStruct(mss)
Console.WriteLine(vbNewLine + "Buffer after Unicode function call: {0}", _
mss.buffer )
Dim buffer2 As New StringBuilder("content", 100)
buffer2.Append(ChrW(0))
buffer2.Append("*", buffer2.Capacity - 8)
Dim mss2 As MyStrStruct2
mss2.buffer = buffer2.ToString()
mss2.size = mss2.buffer.Length
LibWrap.TestStringInStructAnsi(mss2)
Console.WriteLine(vbNewLine + "Buffer after Ansi function call: {0}", mss2.buffer)
End Sub
End Class
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);
}
}
public ref 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 = gcnew 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(mss);
Console::WriteLine( "\nBuffer after Unicode function call: {0}",
mss.buffer );
StringBuilder^ buffer2 = gcnew 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(mss2);
Console::WriteLine("\nBuffer after Ansi function call: {0}",
mss2.buffer);
}
};