我有以下代码:
class Generic
{
[DllImport("Generic.dll", EntryPoint = "Consult", CallingConvention = CallingConvention.Winapi)]
public static extern String Consulta(int NumeroSecao);
}
和
private void Button_Click(object sender, RoutedEventArgs e)
{
Random rnd = new Random();
int random = rnd.Next(9999);
Stopwatch sw = new Stopwatch();
sw.Start();
String teste = Generic.Consult(random);
sw.Stop();
TextoLog = "Tempo de Execução:"+sw.Elapsed.Milliseconds+"ms | ConsultarSAT";
tempoEntreComandos();
}
DLL的代码是:
__declspec(dllexport) char* __stdcall Consult(int numeroSessao)
{
memset(pcReturn,0,sizeof(char) * BUFFER_SIZE);
HANDLE fileHandle;
Communicate(&fileHandle, pcReturn,10);
return pcReturn;
}
当我第二次调用函数Consult
时,收到的消息是Access Violation Exception
,就会出现问题。这里发生了什么?
答案 0 :(得分:1)
解决方案是函数声明中返回的类型,而不是使用String
必须使用IntPtr
。
答案 1 :(得分:1)
必须封送本地字符串才能在c#中使用。您的本机代码实际上并不返回字符串对象,而是返回char指针。你必须告诉编组人员返回类型是什么,如下:
[DllImport("Generic.dll", EntryPoint = "Consult", CallingConvention = CallingConvention.Winapi)]
[return: MarshalAs(UnmanagedType.LPStr)]
public static extern String Consulta(int NumeroSecao);
将LPStr用于ASCII字符串,将LPWStr用于unicode。
实际上,当编组器在转换后立即释放本机字符串时,手动编组字符串可能是更好的主意。声明将是
[DllImport("Generic.dll", EntryPoint = "Consult", CallingConvention = CallingConvention.Winapi)]
public static extern IntPtr Consulta(int NumeroSecao);
你手动将IntPtr编组为字符串,如此
String str = Marshal.PtrToStringAnsi(strptr); // for ansi
String str = Marshal.PtrToStringUni(strptr); // for unicode