I have an issue when implementing OpenCV's K-Nearest to Objective-C++
Below is my sample code for implementation:
BridgeClass.h
#ifndef BridgeClass_h
#define BridgeClass_h
#include <Foundation/Foundation.h>
#interface BridgeClass : NSObject
- (void)testFunction;
#end
#endif
BridgeClass.mm
using namespace ml;
typedef KNearest KNN;
#implementation BridgeClass{
KNN* kNearest;
}
- (id) init {
self = [super init];
if (self) {
kNearest = KNN::create();
}
return self;
}
- (void) testFunction {
BOOL test = kNearest->isTrained();
NSLog(#"Test: %d", test);
}
But when I called testFunction, it shows error:
Thread 1: EXC_BAD_ACCESS (code=1, address=0x400000048)
What is the problem with my implementation?
Related
I am learning Objective-C inheritance and my program is getting lost in a recursive loop and won't come out. It gets hung up when calling a getter function.
I am using XCode version: Version 6.2 (6C101)
My program is given below
Vehicle.h
#ifndef exercise_2_Vehicle_h
#define exercise_2_Vehicle_h
#import <Foundation/Foundation.h>
#interface Vehicle : NSObject
#property float speed;
-(void) start;
-(void) stop;
-(void) park;
#end
#endif
Vehicle.m
#import "Vehicle.h"
#implementation Vehicle
-(void) setSpeed:(float)speed {
self.speed = speed;
}
-(float) speed {
return self.speed;
}
-(void) start {
NSLog(#"Starting the vehicle");
}
-(void) stop {
NSLog(#"Stopping the vehicle");
}
-(void) park {
NSLog(#"Parking the vehicle");
}
#end
Car.h
#ifndef exercise_2_Car_h
#define exercise_2_Car_h
#import "Vehicle.h"
#interface Car : Vehicle
#property (nonatomic) NSString* make;
-(Car*) initMake: (NSString*) make;
-(NSString*) make;
#end
#endif
Car.m
#import "Car.h"
#implementation Car
-(Car*) initMake:(NSString *)make {
self = [super init];
if (self) {
self.make = make;
}
return self;
}
-(NSString*) make {
return self.make;
}
#end
main.m
#import <Foundation/Foundation.h>
#import "Car.h"
#import "Vehicle.h"
int main(int argc, const char * argv[]) {
#autoreleasepool {
// insert code here...
Car* car = [[[Car alloc] init] initMake: #"Camry"];
//[car setSpeed:45];
NSLog(#"The model initialized is ");
[car make];
// [car speed];
}
return 0;
}
The issue you have is caused by creating the property for speed:
#property float speed;
and overriding setSpeed: method.
When you create #property compiler adds two methods for you, in your example setSpeed and speed.
This command:
self.speed = speed;
is equal to:
[self setSpeed: speed];
and inside setSpeed you have this command again which cause the loop. In your example you can remove both methods (setSpeed and speed) because compiler will add it for you. If you need it because you want to do some customisation you should use _speed instead self.speed.
_speed is backed variable added by compiler when using #property.
Change your method to:
-(void) setSpeed:(float)speed {
_speed = speed;
}
to remove the infinite loop.
In the
- (NSString*)make;
use
return _make
instead. The same with the speed.
If you return "self.x" in a getter method, then it's going to try and call the method again because you're requesting it on self. XCode will automatically convert the properties into variables that can be accessed with an '_' character, so you don't need to do any extra work.
You could also ignore our advice and remove both the "speed" and "make" getter methods you have made, because XCode automagically creates them for you.
I am using XCTest to do unit test of some c++/OC mixed codes. I found it seems that XCTAssertThrows cannot catch c++ exception?
My usage is very simple
say, an expression like in c++ test()
XCTAssertThrows(test(), "has throws")
Any suggestion?
Short Answer: wrap it by yourself
Long Answer: you can wrap an NSException for any std::exception, like this
#import <XCTest/XCTest.h>
#import <exception>
#interface NSException (ForCppException)
#end
#implementation NSException (ForCppException)
- (id)initWithCppException:(std::exception)cppException
{
NSString* description = [NSString stringWithUTF8String:cppException.what()];
return [self initWithName:#"cppException" reason:description userInfo:nil];
}
#end
#interface XCTestCase (ForCppException)
#end
#implementation XCTestCase (ForCppException)
- (void)rethowNSExceptionForCppException:(void(^)())action {
try {
action();
} catch (const std::exception& e) {
#throw [[NSException alloc] initWithCppException:e];
}
}
#end
#define XCTAssertCppThrows(expression, format...) \
XCTAssertThrows([self rethowNSExceptionForCppException:^{expression;}], ## format)
Use it like this:
#pragma mark - test
void foo() {
throw std::exception();
}
void bar() {
}
#interface testTests : XCTestCase
#end
#implementation testTests
- (void)testExample
{
XCTAssertCppThrows(foo(), #"should thow exception"); // succeed
XCTAssertCppThrows(bar(), #"should thow exception"); // failed
}
#end
I was reading this article by Jeff Kelley and trying to do the same. However the code was written before ARC was adopted and now fails to compile.
http://blog.slaunchaman.com/2011/04/11/fun-with-the-objective-c-runtime-run-code-at-deallocation-of-any-object/
The main problem is in this part of the printout, some casting errors and then blocked release messages. I found it to be a very interesting example but I can't seem to get it to work.
The problems are:
0. Autosynthesized property 'block' will use synthesized instance variable '_block', not existing instance variable 'block' on the #implementation JKBlockExecutor
1. Cast of block pointer type 'voidBlock' (aka 'void (^)(void)') to C pointer type 'const void *' requires a bridged cast and Cast of C pointer type 'void *' to block pointer type 'typeof (aBlock)' (aka 'void (^__strong)(void)') requires a bridged cast" on the block = Block_copy(aBlock); line
2. Cast of block pointer type 'voidBlock' (aka 'void (^)(void)') to C pointer type 'const void *' requires a bridged cast on Block_release(block);
typedef void (^voidBlock)(void);
#interface JKBlockExecutor : NSObject {
voidBlock block;
}
#property (nonatomic, readwrite, copy) voidBlock block;
- (id)initWithBlock:(voidBlock)block;
#end
#implementation JKBlockExecutor
#synthesize block;
- (id)initWithBlock:(voidBlock)aBlock
{
self = [super init];
if (self) {
block = Block_copy(aBlock);
}
return self;
}
- (void)dealloc
{
if (block != nil) {
block();
Block_release(block);
}
[super dealloc];
}
#end
This is where he creates a category on NSObject.
const void *runAtDeallocBlockKey = &runAtDeallocBlockKey;
#interface NSObject (JK_RunAtDealloc)
- (void)runAtDealloc:(voidBlock)block;
#end
#implementation NSObject (JK_RunAtDealloc)
- (void)runAtDealloc:(voidBlock)block
{
if (block) {
JKBlockExecutor *executor = [[JKBlockExecutor alloc] initWithBlock:block];
objc_setAssociatedObject(self,
runAtDeallocBlockKey,
executor,
OBJC_ASSOCIATION_RETAIN);
[executor release];
}
}
#end
This is how you execute the example.
NSObject *foo = [[NSObject alloc] init];
[foo runAtDealloc:^{
NSLog(#"Deallocating foo!");
}];
[foo release];
Or another way to get other information.
NSObject *foo = [[NSObject alloc] init];
__block id objectRef = foo;
[foo runAtDealloc:^{
NSLog(#"Deallocating foo at address %p!", objectRef);
}];
[foo release];
Can this code be fixed somehow? I took out all the release messages to no avail.
Code below builds and works (or at least seems so), and prints "Deallocating foo!" when I expect it to print it. Part 1:
typedef void (^voidBlock)(void);
#interface JKBlockExecutor : NSObject {
voidBlock block;
}
#property (nonatomic, readwrite, copy) voidBlock block;
- (id)initWithBlock:(voidBlock)block;
#end
#implementation JKBlockExecutor
#synthesize block = block;
- (id)initWithBlock:(voidBlock)aBlock
{
self = [super init];
if (self) {
block = [aBlock copy];
}
return self;
}
- (void)dealloc
{
if (block != nil) {
block();
block = nil;
}
}
#end
Part 2:
const void *runAtDeallocBlockKey = &runAtDeallocBlockKey;
#interface NSObject (JK_RunAtDealloc)
- (void)runAtDealloc:(voidBlock)block;
#end
#implementation NSObject (JK_RunAtDealloc)
- (void)runAtDealloc:(voidBlock)block
{
if (block) {
JKBlockExecutor *executor = [[JKBlockExecutor alloc] initWithBlock:block];
objc_setAssociatedObject(self,
runAtDeallocBlockKey,
executor,
OBJC_ASSOCIATION_RETAIN);
}
}
#end
Testing if it works:
#autoreleasepool {
NSObject *foo = [[NSObject alloc] init];
[foo runAtDealloc:^{
NSLog(#"Deallocating foo!");
}];
}
EDIT
Changed Block_release(block); to block = nil;
If you want to know more about the code below ,please go to Fun With the Objective-C Runtime: Run Code at Deallocation of Any Object
Part 1：create one class: the object We Want To Be Released When That Happens--- this class is like an event：when the target obj dealloc,it happens。use block to execute the event 。
// .m file
// http://weibo.com/luohanchenyilong/
// https://github.com/ChenYilong
// the object We Want To Be Released When That Happens--- this class is like an event：when the target obj dealloc,it happens。use block to execute the event 。
typedef void (^voidBlock)(void);
#interface CYLBlockExecutor : NSObject
- (id)initWithBlock:(voidBlock)block;
#end
// .m file
// http://weibo.com/luohanchenyilong/
// https://github.com/ChenYilong
// the object We Want To Be Released When That Happens--- this class is like an event：when the target obj dealloc,it happens。use block to execute the event 。
#import "CYLBlockExecutor.h"
#interface CYLBlockExecutor() {
voidBlock _block;
}
#implementation CYLBlockExecutor
- (id)initWithBlock:(voidBlock)aBlock
{
self = [super init];
if (self) {
_block = [aBlock copy];
}
return self;
}
- (void)dealloc
{
_block ? _block() : nil;
}
#end
Part 2：core code：use runtime to realize cyl_runAtDealloc method
// CYLNSObject+RunAtDealloc.h file
// http://weibo.com/luohanchenyilong/
// https://github.com/ChenYilong
// use runtime to realize cyl_runAtDealloc method
#import "CYLBlockExecutor.h"
const void *runAtDeallocBlockKey = &runAtDeallocBlockKey;
#interface NSObject (CYLRunAtDealloc)
- (void)cyl_runAtDealloc:(voidBlock)block;
#end
// CYLNSObject+RunAtDealloc.m file
// http://weibo.com/luohanchenyilong/
// https://github.com/ChenYilong
// use runtime to realize cyl_runAtDealloc method
#import "CYLNSObject+RunAtDealloc.h"
#import "CYLBlockExecutor.h"
#implementation NSObject (CYLRunAtDealloc)
- (void)cyl_runAtDealloc:(voidBlock)block
{
if (block) {
CYLBlockExecutor *executor = [[CYLBlockExecutor alloc] initWithBlock:block];
objc_setAssociatedObject(self,
runAtDeallocBlockKey,
executor,
OBJC_ASSOCIATION_RETAIN);
}
}
#end
How to use :
#import "CYLNSObject+RunAtDealloc.h"
then
NSObject *foo = [[NSObject alloc] init];
[foo cyl_runAtDealloc:^{
NSLog(#"Deallocating foo!");
}];
I am trying to make a new Objective-C root class on the GNU runtime. Here is what I have so far:
foo.h:
#include <objc/objc.h>
#interface Foo {
Class isa;
int bar;
}
+ (id) alloc;
+ (id) newWithBar: (int) bar;
- (id) initWithBar: (int) bar;
- (void) p;
- (void) dispose;
#end
foo.m:
#import <foo.h>
#include <stdio.h>
#implementation Foo
+ (id) alloc {
return class_createInstance(self, 0);
}
+ (id) newWithBar: (int) bar {
return [[self alloc] initWithBar: bar];
}
- (id) initWithBar: (int) bar_ {
bar = bar_;
}
- (void) p {
printf ("bar=%d\n", self->bar);
}
- (void) dispose {
object_dispose(self);
}
#end
and a little test program, main.m:
#import <foo.h>
int main(int argc, char *argv[]) {
Foo *foo = [Foo newWithBar: 3];
[foo p];
[foo dispose];
return 0;
}
When I compile foo.m, I get the following warning:
foo.m: In function ‘+[Foo alloc]’:
foo.m:7:3: warning: return makes pointer from integer without a cast [enabled by default]
Why? When I dive into the header files, I can see that class_createInstance returns id. What am I doing wrong here?
You need to include the header for the objective C runtime. The default behaviour of the compiler is to assume undeclared functions return an int.
#include <objc-auto.h>
Sorry - answer above is for OS X/iOS. For GNU you need to include runtime.h as well as objc.h
#include <objc/runtime.h>
I'm trying to wrap a C API in Objective-C but am getting EXC_BAD_ACCESS in objc_release.
Field.h:
#ifdef __cplusplus
extern "C" {
#endif
struct sc_field
{
char *title;
};
typedef struct sc_field sc_field_t;
sc_field_t* sc_create_field();
void sc_destroy_field(sc_field_t *field);
const char* sc_get_title(const sc_field_t *field);
void sc_set_title(sc_field_t *field, const char *title);
#ifdef __cplusplus
}
#include <string>
class Field
{
public:
explicit Field();
virtual ~Field();
std::string title() const;
void setTitle(const std::string &title);
private:
class Private;
Private *d;
};
Field.c:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "Field.h"
sc_field_t* sc_create_field()
{
sc_field_t *field = (sc_field_t*)malloc(sizeof(sc_field_t));
field->title = (char*)calloc(1, sizeof(char));
return field;
}
void sc_destroy_field(sc_field_t *field)
{
if (field)
{
free(field->title);
free(field);
}
}
const char* sc_get_title(const sc_field_t *field)
{
if (!field)
{
fprintf(stderr, "%s: fatal error, field is NULL\n", __FUNCTION__);
return NULL;
}
return field->title;
}
void sc_set_title(sc_field_t *field, const char *title)
{
if (!field)
{
fprintf(stderr, "%s: fatal error, field is NULL\n", __FUNCTION__);
return;
}
field->title = (char*)realloc(field->title, sizeof(char) * sizeof(title));
strcpy(field->title, title);
}
SCField.h:
#import "Field.h"
#import <Foundation/Foundation.h>
#interface SCField : NSObject
{
#private
sc_field_t *field;
}
#property (nonatomic, copy) NSString *title;
- (id)init;
- (id)initWithTitle:(NSString *)title;
- (void)dealloc;
#end
SCField.m:
#import "SCField.h"
#implementation SCField
#synthesize title;
- (id)init
{
self = [super init];
if (self)
{
field = sc_create_field();
}
return self;
}
- (id)initWithTitle:(NSString *)aTitle
{
self = [self init];
if (self)
{
[self setTitle:aTitle];
}
return self;
}
- (void)dealloc
{
sc_destroy_field(field);
[super dealloc];
}
- (NSString *)title
{
return [NSString stringWithUTF8String:sc_get_title(field)];
}
- (void)setTitle:(NSString *)aTitle
{
sc_set_title(field, [aTitle UTF8String]);
}
#end
Test:
SCField *field = [[SCField alloc] initWithTitle:#"Hello world!"];
NSLog(#"%#\n", [field title]);
[field release];
The code seems to work fine until I release my SCField instance. If I remove the title and setTitle: implementations as if I were storing an NSString* directly in the SCField the code works fine (I tried assign instead of copy in the #property, too - no luck). What am I doing wrong?
I think the issue is that calling UTF8String will give you memory that will be autoreleased (according to the documentation).
Rather than using realloc() in sc_set_title(), just malloc() a new buffer and copy it. Also, your realloc() parameters are incorrect anyway, so it probably ends up being a no-op. You need to allocate strlen(title) + 1; sizeof won't do anything for you since you're just asking the compiler to give you 1 (sizeof(char)) * 4 bytes (sizeof(title) - a pointer).
Use getCString:maxLength:encoding:. To get length of string in bytes for a buffer, use lengthOfBytesUsingEncoding: (takes O(n) time) or maximumLengthOfBytesUsingEncoding: (takes O(1) time).