'string' file not found on ios plugin with C++ file - c++

Question

I am trying running c++ file on plugin IOS (not ios app). First I create cpp file
Greeting.cpp
#include "Greeting.hpp"
Greeting::Greeting() {
greeting = "Hello C++!";
}
std::string Greeting::greet() {
return greeting;
}
Then I create Greeting.hpp
#ifndef Greeting_hpp
#define Greeting_hpp
#include <stdio.h>
#include <string>
class Greeting {
std::string greeting;
public:
Greeting();
std::string greet();
};
#endif /* Greeting_hpp */
Then I import it into object c file
AgoraRtcEnginePlugin.m
#import "Greeting.hpp"
NSString* newTitle = [NSString stringWithCString:greeting.greet().c_str() encoding:[NSString defaultCStringEncoding]];
result(newTitle);
But when I complile It always throws errors
/agora-flutter-sdk/ios/Classes/Greeting.hpp:13:10: fatal error: 'string' file not found
#include <string>

Answer 1

The problem you have is that you're including C++ in your Objective-C (AgoraRtcEnginePlugin.m = .m extension is Objective-C) file. Objective-C is a layer on top of C and Objective-C is a strict superset of C.
You can't do this unless you use extern "C", etc. There are questions about this:
How to call C++ function from C?
Calling “C++” class member function from “C” code
etc.
You're not forced to create an C API for you class, because there's also Objective-C++ (.mm extension) and you can use C++ directly in these files.