C ++，Xcode，头文件的链接器错误

Question

I'm learning C++ using Xcode however I always get a linker error when I try to initialize a class in a header file. Here is main.cpp:

#include <iostream>
#include <fstream>
#include "main.h"

using namespace std;
int main() {
    Rectangle rect(4, 5);
    cout << rect.area() << endl;
    return 0;
}

and main.h ...

#ifndef main_h
#define main_h
using namespace std;

class Rectangle {
    int width,height;
public:
    Rectangle(int,int);
    int area() {return width*height;}
};

Rectangle::Rectangle (int x, int y) { width=x; height=y; }

#endif /* main_h */

..and the linker error

clang: error: linker command failed with exit code 1 (use -v to see invocation)

I know Xcode is reading main.h because I used to get a "file not found" error (as well a bunch of others) but I fixed all of that and no longer get those errors. From what I understand Xcode is not able to build the machine code from these 2 files for some reason because if I just copy/paste all the code into one file it does work.

Answer 1

I was able to get this to build and run, both from the command line:

% clang++ main.cpp
% ./a.out
20

and from XCode. With XCode, it wants to find your main.h as part of the project, so it should show up in the project directory next to main.cpp :

You can just drag the file into the project. If that's not your issue, than I don't have any other suggestions for you, hopefully others do.