C# using my own C++/CLI DLL: Error: 'mytrainOp' is not supported by the language -

my c++ class has 1 method:

string mythreadscpp::mythreadscppclass::train(){      double sum = 0.0;     long max = 100 * 1000;     int perc = 0;;      (long n = 0; n < max; n++){         sum += 4.0*pow(-1.0, n) / (2 * n + 1.0);         int rem = n % (max/10);         if (rem == 0){             perc = 100 * n / max;             cout << perc << "%" << endl;         }     }     cout << "100%" << endl;     ostringstream oss;     oss << "result = " << sum;     return oss.str(); } 

it works fine.

c++/cli class library has 1 method:

string threadscppwrapper::threadscppwrapperclass::mytrainop(int% i){     i++;         return ptr->train(); } 

it builds fine.

c# code consuming dll:

namespace threadscsharp {     public partial class frmmain : form     {        private void btntrain_click(object sender, eventargs e)         {             threadscppwrapperclass obj = new threadscppwrapperclass();             int = 5;             obj.mytrainop(i); /* error */         }     } } 

intellisense errors above line: error 1 no overload method 'mytrainop' takes 1 arguments error 2
pointers , fixed size buffers may used in unsafe context

experts, please help.

it not great error message, c# compiler struggles mightily when trying figure out std::string object return. hidden in c# program since don't use it. doesn't matter, compiler still needs deal it.

you must return managed string instead, this:

string^ threadscppwrapper::threadscppwrapperclass::mytrainop(int% i){     i++;     return gcnew string(ptr->train().c_cstr()); } 

and of course if don't have use string declare return value type void. next error 1 reminds pass argument ref, can figure 1 out.