c++, Call dll function with string reference/pointer

I have a solution with two projects, one DLL and one console app. The console app is a client to call and test functions in the DLL.

For the first function greetings, I have faced a problem. I should mention that I am totally new to C and C++.

The DLL project (called plugin) looks like this:

plugin.h

#include "types.h" // which contains S32 and #include<string>
#define EXPORT extern "C" __declspec (dllexport)
EXPORT S32 WINAPI _3Greetings(string *str);

plugin.cpp

#include "plugin.h"
S32 __stdcall _3Greetings(string *str)
{
    *str = "Hello From Plugin!";
    return -1;
}

All DLL functions should return -1 on success or [1-255] on failure. Also, the project has plugin.def to solve name decorating of the __stdcall calling convention.

The console app looks like this:

typedef U32(*GetGreetings)(string);    
HMODULE DllHandler = ::LoadLibrary(L"plugin.dll");
        if (DllHandler != NULL) {
            string greetingText;
            GetGreetings greetings = reinterpret_cast<GetGreetings>(GetProcAddress(DllHandler2, "_3Greetings"));
            greetings(&greetingText); // THE PROBLEM HERE
            cout << greetings << endl;
        }

The problem is if I add & to greetingText, I get an error:

E0415 no suitable constructor exists to convert from "std::string *" to "std::basic_string, std::allocator>"

And also:

C2664 'U32 (std::string)': cannot convert argument 1 from 'std::string *' to 'std::string'

If I do not put the &, I get a runtime exception:

Exception thrown at 0x0FA65A72 (plugin.dll) in ConsoleApp.exe: 0xC0000005: Access violation writing location 0xCCCCCC00.

The typedef for GetGreeting is wrong, it misses a *