function non recognized in objective-C - c++

Question

I'm new to IOS developing but this problem i'm facing does not seem logical to me. I'm declaring a function in both ViewController.h and ViewController.mm (changed to.mm because i'm using C++) but when i call it in ViewController.mm i get use of undeclared identifier error.
Here's the declaration in the header file:
#import <UIKit/UIKit.h>
#import <opencv2/highgui/cap_ios.h>
using namespace cv;
#interface ViewController : UIViewController<CvVideoCameraDelegate>
{
IBOutlet UIImageView* imageview;
CvVideoCamera* videoCamera;
IBOutlet UILabel *label;
}
- (UIImage *) CVMatToImage:(cv::Mat) matrice;
#property (nonatomic, retain) CvVideoCamera* videoCamera;
-(IBAction)cameraStart:(id)sender;
-(IBAction)cameraStop:(id)sender;
#end
and the definition in the .mm file:
- (UIImage *) CVMatToImage:(cv::Mat) matrice
{
NSData *data = [NSData dataWithBytes:matrice.data length:matrice.elemSize()*matrice.total()];
CGColorSpaceRef colorSpace;
CGBitmapInfo bitmapInfo;
if (matrice.elemSize() == 1) {
colorSpace = CGColorSpaceCreateDeviceGray();
bitmapInfo = kCGImageAlphaNone | kCGBitmapByteOrderDefault;
} else {
colorSpace = CGColorSpaceCreateDeviceRGB();
bitmapInfo = kCGBitmapByteOrder32Little | (
matrice.elemSize() == 3? kCGImageAlphaNone : kCGImageAlphaNoneSkipFirst
);
}
CGDataProviderRef provider = CGDataProviderCreateWithCFData((__bridge CFDataRef)data);
// Creating CGImage from cv::Mat
CGImageRef imageRef = CGImageCreate(
matrice.cols, //width
matrice.rows, //height
8, //bits per component
8 * matrice.elemSize(), //bits per pixel
matrice.step[0], //bytesPerRow
colorSpace, //colorspace
bitmapInfo, // bitmap info
provider, //CGDataProviderRef
NULL, //decode
false, //should interpolate
kCGRenderingIntentDefault //intent
);
// Getting UIImage from CGImage
UIImage *finalImage = [UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);
CGDataProviderRelease(provider);
CGColorSpaceRelease(colorSpace);
return finalImage;
}
But when i call it inside an IBAction i get an error
-(IBAction)cameraStop:(id)sender
{
[self.videoCamera stop];
//////////////////////
// Don't forget to process image here
//////////////////////
UIImage *finalImageToOCR = CVMatToImage(cvMatrice);
[imageview setImage:finalImageToOCR];
G8Tesseract *tesseract = [[G8Tesseract alloc] initWithLanguage:#"fra"];
[tesseract setImage:finalImageToOCR];
[tesseract recognize];
NSLog(#"%#", [tesseract recognizedText]);
label.text = [NSString stringWithFormat:[tesseract recognizedText]];
}

Answer 1

You have defined an instance method and not a function. Like the other method calls in your code you need to use a method call along the lines of:
UIImage *finalImageToOCR = [<object instance> CVMatToImage:cvMatrice];
Alternatively if you want a function you would declare is as:
UIImage *CVMatToImage(cv::Mat matrice) { ... }
in which case the function cannot access any instance variables.
HTH