为什么在调用[myclass alloc] misx c ++到object-c ++到object-c时出错？

如何解决为什么在调用[myclass alloc] misx c ++到object-c ++到object-c时出错？

我尝试从对象c使用调用c ++
使用B4I 此代码，但我得到错误 我已经在使用file.mm

此文件Greeting.cpp

#include "Greeting.hpp"

Greeting::Greeting() {
    greeting = "Hello C++!";
}

std::string Greeting::greet() {
    return greeting;
}

---

此文件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 */

---

此文件ViewController.h

---

    #import <UIKit/UIKit.h>

@interface ViewController : UIViewController

- (void)showGreeting;

@end

---

此文件ViewController.mm

---

#import "ViewController.h"
#import "Greeting.hpp"

@interface ViewController ()
{
    Greeting greeting;
    IBOutlet UIButton *helloButton;
}
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view,typically from a nib.
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // dispose of any resources that can be recreated.
}

- (void)showGreeting {

 NSLog(@"test %@");

}


@end

---

我尝试称呼它

---

 ViewController* ViewController1= [[ViewController alloc] init];
  [ ViewController1 showGreeting ];

---

我收到错误未知方法

-------------------------------
Undefined symbols for architecture arm64:
  "_OBJC_CLASS_$_ViewController",referenced from:
      objc-class-ref in b4i_main.o
ld: symbol(s) not found for architecture arm64
clang: error: linker command Failed with exit code 1 (use -v to see invocation)
---------------------------------

当我使用

ViewController* ViewController1;
  [ ViewController1 showGreeting ];

返回null 注意此示例HelloCpp-master

谢谢

解决方法

以下示例显示了如何使用AppDelegate中的方法从objc应用程序调用c ++类。它可以在终端中运行，方法是先将源代码保存在名为“ greet.mm”的文件中，然后使用以下命令：clang greet.mm -framework Cocoa -o greet && ./greet

//clang greet.mm -framework Cocoa -o greet && ./greet

#import <Cocoa/Cocoa.h>

class Greeting {
public:
  void greet();
};

void Greeting::greet() {
  NSLog(@"Hello C++!");
}

@interface AppDelegate : NSObject <NSApplicationDelegate>
{
  NSWindow *window;
}
- (void) myBtnAction: (id)sender;
- (void) buildMenu;
- (void) buildWnd;

@end

@implementation AppDelegate

- (void) myBtnAction: (id)sender {
  Greeting g;
  g.greet();
}

- (void) buildMenu {
 NSMenu *menubar = [NSMenu new];
 NSMenuItem *menuBarItem = [NSMenuItem new];
 [menubar addItem:menuBarItem];
 [NSApp setMainMenu:menubar];
 NSMenu *appMenu = [NSMenu new];
 NSMenuItem *quitMenuItem = [[NSMenuItem alloc] initWithTitle:@"Quit"
 action:@selector(terminate:) keyEquivalent:@"q"];
 [appMenu addItem:quitMenuItem];
 [menuBarItem setSubmenu:appMenu];
}

- (void) buildWnd {    
#define _wndW  200
#define _wndH  150
 window = [ [ NSWindow alloc ] initWithContentRect:NSMakeRect( 0,_wndW,_wndH )
    styleMask: NSWindowStyleMaskClosable | NSWindowStyleMaskTitled
    backing:NSBackingStoreBuffered defer:YES];
 [window center];
 [window setTitle: @"Test window" ];
 [window makeKeyAndOrderFront:nil];
    
// **** My Button **** //
 NSButton *myBtn =[[NSButton alloc]initWithFrame:NSMakeRect( 40,80,125,24 )];
 [myBtn setBezelStyle:NSBezelStyleRounded ];
 [myBtn setTitle: @"Run CPP Class"];
 [myBtn setAction: @selector (myBtnAction:)];
 [[window contentView] addSubview: myBtn];

// **** Quit btn **** //
 NSButton *quitBtn = [[NSButton alloc]initWithFrame:NSMakeRect( _wndW - 50,10,40,40 )];
 [quitBtn setBezelStyle:NSBezelStyleCircular ];
 [quitBtn setTitle: @"Q" ];
 [quitBtn setAction:@selector(terminate:)];
 [[window contentView] addSubview: quitBtn];
}

- (void) applicationWillFinishLaunching: (NSNotification *)notification {
[self buildMenu];
[self buildWnd];
}

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
  // Insert code here to initialize your application
}

@end

int main () {
 NSApplication *app = [NSApplication sharedApplication];
 AppDelegate *appDelegate = [[AppDelegate alloc] init];
 [app setDelegate:appDelegate];
 [NSApp run];
 return 0;
}

,

应在iOS中运行。将ViewController的扩展名从.m更改为.mm

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController
@end

#import "ViewController.h"

class Greeting {
public:
  void greet();
};

void Greeting::greet() {
  NSLog(@"Hello C++!");
}

@interface ViewController ()
@property (strong,nonatomic) IBOutlet UIButton *LaunchBtn;

@end

@implementation ViewController
- (IBAction)showGreeting:(id)sender {
  Greeting g;
  g.greet();
}

- (void)viewDidLoad {
  [super viewDidLoad];
  // Do any additional setup after loading the view.
}

@end