“字符串”示例
该示例说明如何使用从非托管函数返回的字符串，以及如何传递包含 Unicode 格式或 ANSI 格式的字符串的结构。 它还显示如何正确地初始化这些字符串以及如何检索返回值。
String 示例使用以下非托管函数（这里同时显示其原始函数声明）：
从 PinvokeLib.dll 导出的 TestStringAsResult。
char* TestStringAsResult();从 PinvokeLib.dll 导出的 TestStringInStruct。
void TestStringInStruct(MYSTRSTRUCT* pStruct);从 PinvokeLib.dll 导出的 TestStringInStructAnsi。
void TestStringInStructAnsi(MYSTRSTRUCT2* pStruct);
PinvokeLib.dll 是一个自定义非托管库，它包含前面列出的函数的实现以及两种结构 MYSTRSTRUCT 和 MYSTRSTRUCT2。 这些结构包含以下元素：
typedef struct _MYSTRSTRUCT
{
wchar_t* buffer;
UINT size;
} MYSTRSTRUCT;
typedef struct _MYSTRSTRUCT2
{
char* buffer;
UINT size;
} MYSTRSTRUCT2;
在此示例中，托管 MyStrStruct 和 MyStrStruct2 结构包含托管字符串而不是 StringBuilder 缓冲区，原因是 StringBuilder 类型不能在结构内部使用。 StructLayoutAttribute 特性经过设置，可确保成员在内存中按它们的出现顺序依次排列。 CharSet 字段经过设置以指定 ANSI 或 Unicode 格式。
LibWrap 类包含由 App 类调用的托管原型方法。 虽然结构通常是通过值传递的，但 TestStringInStruct 和 TestStringInStructAnsi 方法的参数使用 ref（在 Visual Basic 中为 ByRef）关键字来标记，该关键字通过引用传递结构。
声明原型
' 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);
};
调用函数
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);
}
};
请参见
概念
其他资源
Creating Prototypes in Managed Code