I wrote a class library in VS 2010 C++/CLI and created a dll.
// testclass.h
#pragma once
#include <string>
namespace test
{
public ref class testclass
{
public:
std::string getstringfromcpp()
{
return "Hello World";
}
};
}
And I want to use it in C# program, add this dll to reference then:
using test;
...
testclass obj = new testclass();
textbox1.text = obj.getstringfromcpp();
...
What should I do with this issue?
For an interop scenario, you need to return a string object you'll be able to read from .NET code.
Don't return a std::string (there is no such thing in C#) or a const char * (readable from C# but you'd have to manage memory deallocation) or things like that. Return a System::String^ instead. This is the standard string type in .NET code.
This will work:
public: System::String^ getStringFromCpp()
{
return "Hello World";
}
But if you actually have a const char * or std::string object you'll have to use the marshal_as template:
#include <msclr/marshal.h>
public: System::String^ getStringFromCpp()
{
const char *str = "Hello World";
return msclr::interop::marshal_as<System::String^>(str);
}
Read Overview of Marshaling in C++ for more details.
To convert a System::String^ to std::string you can also use the marshal_as template, as explained in the above link. You just need to include a different header:
#include <msclr/marshal_cppstd.h>
System::String^ cliStr = "Hello, World!";
std::string stdStr = msclr::interop::marshal_as<std::string>(cliStr);
In my program somehow it refuses to convert the std::string directly to System::String^ but takes the char* casting ==> std::string.c_str()
public: System::String^ getStringFromCpp()
{
std::string str = "Hello World";
return msclr::interop::marshal_as<System::String^>(str.c_str());
}
foo()? Other than that, whats the problem with your code above? It looks like it should work