Esempio di stringhe

Articolo
08/11/2011

In questo esempio viene dimostrato come utilizzare una stringa restituita da una funzione non gestita e come passare una struttura che contiene una stringa formattata con Unicode o con ANSI. Viene mostrato come inizializzare correttamente queste stringhe e come recuperare i valori restituiti.

Nell'esempio di stringa vengono utilizzate le seguenti funzioni non gestite, illustrate con le dichiarazioni di funzione originali:

TestStringAsResult esportata da PinvokeLib.dll.
```
char* TestStringAsResult();
```

TestStringInStruct esportata da PinvokeLib.dll.

void TestStringInStruct(MYSTRSTRUCT* pStruct);

TestStringInStructAnsi esportata da PinvokeLib.dll.

void TestStringInStructAnsi(MYSTRSTRUCT2* pStruct);

PinvokeLib.dll è una libreria non gestita personalizzata contenente implementazioni per le funzioni elencate in precedenza e due strutture, MYSTRSTRUCT e MYSTRSTRUCT2, le quali contengono i seguenti elementi:

typedef struct _MYSTRSTRUCT
{
   wchar_t* buffer;
   UINT size; 
} MYSTRSTRUCT;
typedef struct _MYSTRSTRUCT2
{
   char* buffer;
   UINT size; 
} MYSTRSTRUCT2;

In questo esempio le strutture gestite MyStrStruct e MyStrStruct2 contengono stringhe gestite anziché buffer StringBuilder, poiché il tipo StringBuilder non può essere utilizzato all'interno di una struttura. L'attributo StructLayoutAttribute viene impostato in modo che i membri vengano disposti in sequenza nella memoria, nell'ordine in cui appaiono. Il campo CharSet viene impostato in modo da specificare il formato ANSI o Unicode.

La classe LibWrap contiene i metodi di prototipo gestiti chiamati dalla classe App. Sebbene le strutture vengano in genere passate per valore, gli argomenti per i metodi TestStringInStruct e TestStringInStructAnsi sono contrassegnati con la parola chiave ref (ByRef in Visual Basic), tramite la quale le strutture vengono passate per riferimento.

Dichiarazione dei prototipi

' 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);
};

Chiamata delle funzioni

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);
    }
};

Vedere anche

Concetti

Marshalling di stringhe

Tipi di dati di platform invoke

Marshalling predefinito per le stringhe

Altre risorse

Creating Prototypes in Managed Code

Condividi tramite