Xcode print character not found for my C function, which is used in the Objective-C method body

Question

Xcode build prints this error.

Undefined characters:
"EGViewportDimensionMake (unsigned int, unsigned int, unsigned int, unsigned int)" referenced: - [render render] in Renderer.o ld: character not found collect2: ld returned 1 exit status

I can’t understand what the problem is. I don't understand the classic C syntax. These are function source code files:

EGViewportDimension.h

#import <Foundation/Foundation.h>

struct EGViewportDimension
{
    NSUInteger x;
    NSUInteger y;
    NSUInteger width;
    NSUInteger height;
};
typedef struct EGViewportDimension EGViewportDimension;

EGViewportDimension EGViewportDimensionMake(NSUInteger x, NSUInteger y, NSUInteger width, NSUInteger height);

EGViewportDimension.m

#import "EGViewportDimension.h"

EGViewportDimension EGViewportDimensionMake(NSUInteger x, NSUInteger y, NSUInteger width, NSUInteger height)
{
    EGViewportDimension dim;
    dim.x = x;
    dim.y = y;
    dim.width = width;
    dim.height = height;
    return dim;
}

I referenced and used this as:

Renderer.mm

#import "EGViewportDimension.h"

//.... many codes omitted.

EGViewportDimension vdim = EGViewportDimensionMake(0, 0, backingWidth, backingHeight);

Answer 1

Renderer.mm Renderer.m. ++, Objective-C ++, . ++ Objective-C.

, Objective-C ++ C.

---- () ----

, . : C Objective-C ++?

Answer 2

, . [Renderer render], . , EGViewportDimension.h (, Renderer.m)?