OpenCV Error - Core.hpp header must be compiled as C++

Question

I have tried Core.hpp, Base.hpp header must be compiled as C++ error. I have BITCODE set as NO.

#import <UIKit/UIKit.h>
#import <Foundation/Foundation.h>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>

@interface OpenCV : NSObject
    /// Converts a full color image to grayscale image with using OpenCV.
+ (nonnull UIImage *)cvtColorBGR2GRAY:(nonnull UIImage *)image;
+ (cv::Mat)cvMatFromAdjustedUIImage:(UIImage *)image;
+ (cv::Mat)cvMatFromUIImage:(UIImage *)image;
+ (cv::Mat)cvMatGrayFromUIImage:(UIImage *)image;
+ (cv::Mat)cvMatGrayFromAdjustedUIImage:(UIImage *)image;
@end

In my OpenCVSample.mm I have included #import "OpenCV.h in header.

Git: https://github.com/n1tesh/OpenCV-Demo

.mm files should be complied as objective c++ source in the inspector. — Jack, Sep 19 '17 at 05:54
@Jack Yes. Have changed Type to `Objective-C++ Source` but still the same error. — Nitesh, Sep 19 '17 at 05:57
In build setting search Build Active Architecture Only and set to NO — Prashant Tukadiya, Sep 19 '17 at 06:07
@JonSnow Bridging Header file - `#import "OpenCV.h"` . And tried Build Active Architecture Only - `NO` but still same error. — Nitesh, Sep 19 '17 at 06:09
@Nitesh ignore then , Check this C++ Standard Library: libstdc++ (GNU C++ standard library) — Prashant Tukadiya, Sep 19 '17 at 06:13
Ohh man, final try can be check whether libc++.tbd added to the framework , Other linker flag add -lc++ — Prashant Tukadiya, Sep 19 '17 at 06:18
Yes its already added. I'll create a demo project and share Git link here. — Nitesh, Sep 19 '17 at 06:20
I have downloaded project but i have pod erros you can try this link https://computer-vision-talks.com/2012-06-23-opencv-tutorial-part-1/ — Prashant Tukadiya, Sep 19 '17 at 07:12

score 1 · Accepted Answer · answered Sep 19 '17 at 07:18

What you need is a precompile header file. Create a PrefixHeader.pch file at the same folder with the .xcodeproj file with content:

#ifndef PrefixHeader_pch
#define PrefixHeader_pch

#ifdef __cplusplus
#include "opencv2/opencv.hpp"
// include other opencv2 headers if needed.
#endif

#endif /* PrefixHeader_pch */

Then go to Project's Build Settings, search for Prefix Header and set it to PrefixHeader.pch.

Additionally, if you want to call bridge MMOpenCVHelper.h to your swift code, it has to be Objective-C++ only. Put anything OpenCV, or standard C++, in MMOpenCVHelper.mm. For example:

MMOpenCVHelper.h:

#import <UIKit/UIKit.h>
#import <Foundation/Foundation.h>

// These two headers god to mm file
// #include <opencv2/imgproc/imgproc.hpp>
// #include <opencv2/highgui/highgui.hpp>


@interface MMOpenCVHelper : NSObject
+ (UIImage *) applyOpenCVTo: (UIImage*) uiImage;

// these methods have to be in mm file, hence private
// + (UIImage *)UIImageFromCVMat:(cv::Mat)cvMat;
// + (cv::Mat)cvMatFromAdjustedUIImage:(UIImage *)image;
// + (cv::Mat)cvMatFromUIImage:(UIImage *)image;
// + (cv::Mat)cvMatGrayFromUIImage:(UIImage *)image;
// + (cv::Mat)cvMatGrayFromAdjustedUIImage:(UIImage *)image;


@end

And MMOpenCVHelper.mm:

#import "MMOpenCVHelper.h"
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>

@implementation MMOpenCVHelper

// implementation of public methods:
+ (UIImage *) applyOpenCVTo: (UIImage*) uiImage{
    cv::Mat cvFrame = [MMOpenCVHelper cvMatFromAdjustedUIImage: uiImage];
    // do something with cvFrame using OpenCV
    cv::Mat ret = cvFrame.clone();

    return [MMOpenCVHelper UIImageFromCVMat: ret];
}

// Implementations of the conversion functions:
+ (UIImage *)UIImageFromCVMat:(cv::Mat)cvMat{
    // do something here
    return uiImage;
}

+ (cv::Mat)cvMatFromAdjustedUIImage:(UIImage *)image;
+ (cv::Mat)cvMatFromUIImage:(UIImage *)image;
+ (cv::Mat)cvMatGrayFromUIImage:(UIImage *)image;
+ (cv::Mat)cvMatGrayFromAdjustedUIImage:(UIImage *)image;
@end

Later, in SomeSwiftFile.swift you can do (please verify this since I'm not very familiar with Swift):

let UIImage * processedImage = MMOpenCVHelper.applyOpenCVTo(uiImage);

i still got problem. can u help :(( – famfamfam Aug 15 '18 at 16:50 — famfamfam, Aug 15 '18 at 16:50
But this won't work if you want to inherit a OpenCV class. – Bagusflyer Apr 04 '19 at 07:10 — Bagusflyer, Apr 04 '19 at 07:10

OpenCV Error - Core.hpp header must be compiled as C++

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