如何在 C# 中通过引用创建 dll 函数，接受来自 MQL4 的值并返回它?

Question

这是原始函数：

public  static  void GetEvent ( int event_n, ref  string el_name, ref  int id,   ref  long lparam, ref  double dparam, ref  string sparam)
{         
GuiEvent e = m_global_events [event_n];
el_name = e.el_name;
id = ( int ) e.id;
lparam = e.lparam;
dparam = e.dparam;
sparam = e.sparam;
}

这是我尝试过的：

public  static  void GetEvent ([MarshalAs (UnmanagedType.I4)] int event_n, [MarshalAs (UnmanagedType.LPTStr)] ref  string   el_name, [MarshalAs (UnmanagedType.I4)] ref  int id, [MarshalAs (UnmanagedType.I8)] ref  long lparam, [MarshalAs (UnmanagedType.R8)] ref  double dparam, [MarshalAs (UnmanagedType.LPTStr)] ref  string sparam)
{
GuiEvent e = m_global_events [event_n];
el_name = e.el_name;
Console.WriteLine (e.el_name);
id = ( int ) e.id;
lparam = e.lparam;
dparam = e.dparam;
sparam = e.sparam;
}

我收到一个错误：

Access violation  

请让我知道我能做些什么来让它与 MQL4 一起工作。

像这样访问 Dll ：

#import    "my.dll"  
void GetEvent ( int index, string element_name, int elemnet_id, long element_lparam, double element_dparam, string element_sparam);
#import

Answer 1

我想我可以解决你的问题。
这是：
首先，让我们修复你的 C# Dll 函数：它必须是这样的：

[DllExport("GetEvent", CallingConvention = CallingConvention.StdCall)]
public static void GetEvent([MarshalAs(UnmanagedType.I4)] int event_n, [In, Out, MarshalAs(UnmanagedType.LPWStr)] StringBuilder el_name, [In, Out, MarshalAs(UnmanagedType.I4)] ref int el_id,
[In, Out, MarshalAs(UnmanagedType.I8)]ref long lparam, [In, Out, MarshalAs(UnmanagedType.R8)]ref double dparam, [In, Out, MarshalAs(UnmanagedType.LPWStr)] StringBuilder sparam)
{
GuiEvent e = m_global_events[event_n];
_ = el_name.Replace("-1", e.el_name);
el_id = (int)e.id;
lparam = e.lparam;
dparam = e.dparam;
_ = sparam.Replace("-1", e.sparam);
}

现在修复 C# 函数后，让我们改进您的 MQL4：

#import    "my.dll"  
void GetEvent ( int index, string &element_name, int &elemnet_id, long &element_lparam, double &element_dparam, string &element_sparam);
#import

现在要访问这些值，您必须使用如下所示的内容调用该函数：

void OnInit()
{
string name="-1", sparam="-1";
int id;
long lparam;
double dparam;
GetEvent(0, name, id, lparam, dparam, sparam);
PrintFormat("name: %s, id: %d, lparam: %ld, dparam: %lf, sparam: %s",name, id, lparam, dparam, sparam);
}

我希望这对你有帮助。以下是一些将来对您有所帮助的参考资料： 参考：https://www.mql5.com/en/articles/249、https://www.mql5.com/en/forum/150219 https://www.mql5.com/en/forum/149586