c# - Dllimport 将字符串从 C# 传递到 C++

Question

我正在尝试使用平台调用将字符串从 C# 传递到 C++。

• C++代码:

  #include<string>
  using namespace std;
  
  extern "C" 
  {
       double __declspec(dllexport) Add(double a, double b)
       {
           return a + b;
       }
       string __declspec(dllexport) ToUpper(string s)
       {
           string tmp = s;
           for(string::iterator it = tmp.begin();it != tmp.end();it++)
               (*it)-=32;
           return tmp;
       }
  }
  

• C#代码:

  [DllImport("TestDll.dll", CharSet = CharSet.Ansi, CallingConvention =CallingConvention.Cdecl)]
  public static extern string ToUpper(string s); 
  
  static void Main(string[] args)
  {
      string s = "hello";
      Console.WriteLine(Add(a,b));
      Console.WriteLine(ToUpper(s));
  }
  

我收到一个 SEHException。像这样使用 std::string 是不可能的吗？我应该改用 char* 吗？

Answer 1

正确的决定

C# 端:

[DllImport("CppDll.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern IntPtr GetString(string s);

public string GetString_(string s)
{            
    var ptr = GetString(s);                                
    var answerStr = Marshal.PtrToStringAnsi(ptr);
    return answerStr;
}

C++ 方面:

extern "C" __declspec(dllexport) const char* GetString(char* s)
{       
    string workStr(s);      
    int lenStr = workStr.length() + 1;
    char* answer = new char[lenStr];
    const char * constAnswer = new char[lenStr];
    strcpy(answer, workStr.c_str());
    constAnswer = answer;
    return constAnswer;
}

并在cpp项目的设置中禁用/sdl-。