I am trying to NSLog some enums I have. For example this piece of code prints the integer representation of the enum, but I want it to output the actual string name, in this case MON. How can I do that?
#import <Foundation/Foundation.h>
int main(void)
{
typedef enum {
SUN,
MON,
TUES
} DAYS;
DAYS d = MON;
NSLog(#"%#", d);
return 0;
}
The LLDB debugger will show the string identifiers. So instead of using NSLog you could use a breakpoint with a debugger command action ("p d" in your case) and set the breakpoint to automatically continue after evaluating.
You can configure a breakpoint by right-clicking on the blue marker.
Not easily. The string identifier for an enum value is for the developer, but internally it's simply a value with a particular type (in your example, DAYS).
You could write a translation method, to return the name of the enum value, e.g
- (NSString*)nameForDay:(DAYS)day {
switch (day) {
case SUN:
return #"SUN";
break;
case MON:
return #"MON";
break;
case TUES:
return #"TUES";
break;
default:
return nil;
break;
};
return nil;
}
It's a nasty way of doing it, as it's not wholly resilient to the enum values changing, but its a way to associate a string with an enum value.
Related
I am trying to convert this swift code to Objective-C
convenience init(fromString string: String, format:DateFormat)
{
if string.isEmpty {
self.init()
return
}
let string = string as NSString
switch format {
case .DotNet:
let startIndex = string.rangeOfString("(").location + 1
let endIndex = string.rangeOfString(")").location
let range = NSRange(location: startIndex, length: endIndex-startIndex)
let milliseconds = (string.substringWithRange(range) as NSString).longLongValue
let interval = NSTimeInterval(milliseconds / 1000)
self.init(timeIntervalSince1970: interval)
So far, I am doing this:
-(id) initFromString: (NSString *) string format: (DateFormat *) format{
if (string == nil) {
self = [self init];
return self;
}
switch (format) {
case .DotNet:
NSRange *startIndex = [[string rangeOfString:#"("] location]+1;
}
}
and have already run into the following errors:
for the switch(format): statement requires expression of integer type (DateFormat * __strong' invalid)
and for the 2 following lines: Expected expression
Any ideas ?
In Objective-C, the string is impliedly optional. Testing for nil merely tests whether a string was supplied. It doesn't check whether an empty string was supplied. You probably want to switch to string.length == 0 as, by the magic of nil-messaging, that'll work to check for either an empty string or no string at all.
Objective-C uses C's switch statement. So you can switch on integral types only. If this were Objective-C code originally, DateFormat would probably be an NS_ENUM — an integral type rather than an object type. It looks like the original was an enumeration from your use of dot syntax? If you can make it an Objective-C enumeration then do so and simply use:
- (id)initFromString:(NSString *)string format:(DateFormat)format {
....
switch(format)
{
case DateFormatDotNet: {
....
} break;
}
(with the curly brackets within the case being because you want to declare variables in there).
Otherwise, if it must be an object format then you're looking at a painful construction like:
if([format isEqual:[DateFormat dotNetFormat]]) {
}
else if([format isEqual:[DateFormat otherFormat]]) {
}
... etc ...
Also Objective-C has a syntactic distinction between structs, which are exactly what they are in C — named fields but no built-in behaviour — and object types, which is again because it's a strict superset of C. NSRange is a struct. So square bracket messaging syntax doesn't work on it. Instead of:
[[string rangeOfString:#"("] location]
Use:
[string rangeOfString:#"("].location
Square brackets around the rangeOfString call because it's a message dispatch to an object, then a dot for location because you get back a C struct as a value, and that's how one accesses a field in a C struct.
(dot syntax also works for properties on Objective-C objects, but explicitly to alias to getter and setter calls, and only for about the most recent of Objective-C's three decades)
Assuming this code is related to How to convert a Swift enum: String into an Objective-C enum: NSString?
Since your DateFormat variable is an object with a dateFormatType that is an NSString, you are going to have to use a chained if-else construct to select from the various possibilities:
if([format.dateFormatType compare: DotNetDateFormatType] == NSOrderedSame) {
[self handleDotNetDateFormat: format]
} else if ([format.dateFormatType compare: RSSDateFormatType] == NSOrderedSame) {
[self handleRSSDateFormat: format]
...
Objective-C has no concept of the dot-value syntax for enum values (so ".DotNet" is not a valid term in Objective-C). That's why the compiler is complaining about those either lines.
How can I have a method/function that can return any type? For example sometimes the type will need to be float and sometimes it will need to be NSString* so id won't work because float isn't an id. I am not opposed to doing it in a c or c++ function if it's easier.
The reason why I need a dynamic return type is because I'm using objc/runtime to get an Ivar.
I would like some_type to be able to anything:
- (some_type)getIvarWithName:(const char *)name in:(id)obj
{
Ivar ivar(class_getInstanceVariable(object_getClass(obj),name));
return (some_type)ivar;
}
Return a float wrapped in an NSNumber, then you can use the id return type.
To simplify it, you can even use boxing literals, for example:
return #(1.1f);
The first thing to think about is why you would need a function that can return any type. It really doesn't make sense because you wouldn't be able to assign the value to anything, since you don't know the type. Of course, the situation is different when dealing strictly with Obj-C objects, as the language utilizes unknown objects with the id keyword. Unknown objects are like mixing Honeycrisp apples with Macintosh apples (no pun intended), and what you are trying to do is like mixing Honeycrisp apples with airplanes! However, if you want a certain type returned based off of the parameters (such as returning int for int parameters and float for float parameters), then you can overload the functions. Otherwise, then only way that I know of to return absolutely anything would be a void pointer (void *). This would point to a chunk of data that could really be anything. But back to the original problem. What does it represent and how long is it? Good luck!
UPDATE: As other answers mention, you can wrap simple data types (int, float, etc.) in objects such as NSNumbers or NSValues, which will work for your case. But when extending to more general scenarios with complex types such as structs, these generally can't be wrapped in built-in classes. You would need to make your own class using Obj-C.
There is no polymorphism of that kind in Obj-C.
If you know in advance what will be returned then you could use to methods of course.
Retruning id would work when you use an NSNumber for the float value.
You could even introduce a response object that either carries a number or a string and provides (bool) isNumber and (bool) isString methods for later processing.
But what are you really up to? In which context are you using that and what do you really try to achieve. To me it sounds as if there may be better solutions available.
Ofcourse it's weird solution, but you have weird question.
You need enable objective-c++: rename .m-file to .mm
Then yours code will look something like that:
void weird_function(int a)
{
switch (a)
{
case 0: throw #"Hello";
default: throw a;
}
}
void some_code(int a)
{
try
{
weird_function(a);
}
catch (int a)
{
NSLog(#"Catch int: %d", a);
}
catch (NSString* str)
{
NSLog(#"Catch string: %#", str);
}
}
Yours method can be implemented something like that:
union ValueHolder
{
void* voidPtrValue;
int intValue;
float floatValue;
NSString* nssstringValue;
};
- (void)getIvarWithName:(const char *)name in:(id)obj
{
ValueHolder vh;
Ivar ivar = object_getInstanceVariable(obj,name, &vh.voidPtrValue));
if (NULL == ivar)
return;
const char* encoding = ivar_getTypeEncoding(ivar);
if (0 == strcmp(encoding, #encode(int)))
throw vh.intValue;
if (0 == strcmp(encoding, #encode(float)))
throw vh.floatValue;
if (0 == strcmp(encoding, "#\"NSString\""))
throw vh.nsstringValue;
}
I found that using a template in c++ works to have a custom type
The following code works best for my situation:
template <typename _type>
static inline _type & hookVar(id self, NSString*name)
{
Ivar ivar(class_getInstanceVariable(object_getClass(self),[name UTF8String]));
#if __has_feature(objc_arc)
void *pointer(ivar == NULL ? NULL : reinterpret_cast<char *>((__bridge void *)self) + ivar_getOffset(ivar));
#else
void *pointer(ivar == NULL ? NULL : reinterpret_cast<char *>(self) + ivar_getOffset(ivar));
#endif
return *reinterpret_cast<_type *>(pointer);
}
To call the function I just use something like:
NSWindow *win = hookVar<NSWindow*>(self, #"_window");
I am trying to implement a simple method, however I am still quite a newbie on objective-c.
I have this simple method which is trying to convert from an id to a specific value in enum, if matched.
This is the enum
typedef enum {
DXTypeUnknown = 0,
DXDatasource = 1,
DXGroup = 2
} DXPropertyType;
And this is the relevant method:
-(DXPropertyType)typeFromObject:(id)_type {
int _t = [_type intValue];
switch (_t) {
case DXDatasource:
return [NSNumber numberWithInt:DXDatasource];
case DXGroup:
return [NSNumber numberWithInt:DXGroup];
default:
return [NSNumber numberWithInt:DXTypeUnknown];
}
}
The very first check I would to implement is if the id can be converted to an int, then see if it falls in the two relevant categories group or datasource, or return a default value if not. Could you tell me if the switch/case I implemented is a proper solution or not ?
I would like also this method not to causing crash of an application, so what could be advisable to check, keeping in mind that in any case the default value is to be returned.
thanks
[EDIT]
I forgot to say that this value is going to be stored in a field of a NSManagedObject, which by CoreData restriction can be an NSNumber, so probably there's a better solution instead of an enum.
It might be a good idea to include this code to check if the id can be used:
if (![_type respondsToSelector:#selector(intValue)])
return nil;
However, if you'll always pass a NSNumber go ahead and declare the method as:
- (DXPropertyType)typeFromObject:(NSNumber)_type;
In your code, you're returning a NSNumber. I don't think that's what you really
want, as you'd be doing nothing with the NSNumber passed. Return the enum
item:
-(DXPropertyType)typeFromObject:(id)_type {
if (![_type respondsToSelector:#selector(intValue)])
return nil;
int _t = [_type intValue];
switch (_t) {
case DXDatasource:
return DXDatasource;
case DXGroup:
return DXGroup;
default:
return DXTypeUnknown;
}
}
And then this can be simplified to:
- (DXPropertyType)typeFromObject:(id)_type {
if ([_type respondsToSelector:#selector(intValue)]) {
int t = [_type intValue];
DXPropertyType property_t;
if (t >= 1 && t <= 2)
property_t = t;
else
property_t = DXTypeUnknown;
return property_t;
}
return nil;
}
Your switch statement is a good solution and will not cause a crash.
However, your method returns a NSNumber when it expects a different return. I suggest changing the method to
-(NSNumber)typeFromObject:(id)_type
You specify that your method returns an enum, but you return objects. So either return the enum values or specify the return type to be NSNumber *.
A different solution could be using singleton objects instead of an enum, but that's probably more work than it's worth. Think [NSNull null].
In other dynamic languages like ruby, javascript etc. you can do simply this:
switch(someString) {
case "foo":
//do something;
break;
case "bar":
// do something else;
break;
default:
// do something by default;
}
In objective-c, because it's derived very colsely from c language, you can't do that. My best practice for this is:
#import "CaseDemo.h"
#define foo 1
#define bar 2
static NSMutableDictionary * cases;
#implementation CaseDemo
- (id)init
{
self = [super init];
if (self != nil) {
if (cases == nil) {
// this dict can be defined as a class variable
cases = [[NSMutableDictionary alloc] initWithCapacity:2];
[cases setObject:[NSNumber numberWithInt:foo] forKey:#"foo"];
[cases setObject:[NSNumber numberWithInt:bar] forKey:#"bar"];
}
}
return self;
}
- (void) switchFooBar:(NSString *) param {
switch([[cases objectForKey:param] intValue]) {
case foo:
NSLog(#"its foo");
break;
case bar:
NSLog(#"its bar");
break;
default:
NSLog(#"its default");
break;
}
}
#end
It's seems to be ok, but #define makes foo and bar like a reserved word, and I can't use in my code. If I replace define constants with class constants, this problem is fixed, because in other classes I must use MyClassName before the constant name. But how can I minimize the object allocation for this simple task? Someone have a "better practice" for this?
EDIT:
The code below is what I wanted to do, but it's a little bit unconfortable to get the values of the enum or #define. Because I created an application what have just an input where I can write the string to get that hash and go back to xcode and set the values for the enums. So my problem is I can't do that in runtime time, because of the main behavour of switch case statement... Or if I do that with that NSDictionary way -> its have a lot of overhead compared with this solution.
#import "CaseDemo.h"
typedef enum {
foo = 1033772579,
bar = -907719821
} FooBar;
unsigned int APHash(NSString* s)
{
const char* str = [s UTF8String];
unsigned int len = [s length];
unsigned int hash = 0xAAAAAAAA;
unsigned int i = 0;
for(i = 0; i < len; str++, i++)
{
hash ^= ((i & 1) == 0) ? ( (hash << 7) ^ (*str) * (hash >> 3)) :
(~((hash << 11) + ((*str) ^ (hash >> 5))));
}
return hash;
}
#implementation CaseDemo
- (void) switchFooBar:(NSString *) param {
switch(APHash(param)) {
case foo:
NSLog(#"its foo");
break;
case bar:
NSLog(#"its bar");
break;
default:
NSLog(#"its default");
break;
}
}
#end
NOTE: the hash function can defined elsewhere in common namespace to use it anywhere, typically I create a Utils.h or Common.h for this kind of stuff.
NOTE2: In "real word" we need to use some cryptographic hashing function, but now I used the algorithm by Arash Partow to keep the example simple.
So, my final question: Is there a way to evaluate these values with the preprocessor somehow? I think no, but maybe? :-)
Something like:
// !!!!!! I know this code is not working, I don't want comments about "this is wrong" !!!!
// I want a solution to invoke method with preprocessor, or something like that.
typedef enum {
foo = APHash(#"foo"),
bar = APHash(#"bar")
} FooBar;
UPDATE: I found a "maybe solution" but it seems to be work with g++ 4.6> only. generalized constant expressions may be do it for me. But I'm still testing...
typedef enum {
foo,
bar
} FooBar;
- (void) switchFooBar:(NSString *) param {
switch([[cases objectForKey:param] intValue]) {
case foo:
NSLog(#"its foo");
break;
case bar:
NSLog(#"its bar");
break;
default:
NSLog(#"its default");
break;
}
}
NSString * extension = [fileName pathExtension];
NSString * directory = nil;
NSUInteger index = [#[#"txt",#"png",#"caf",#"mp4"] indexOfObjectPassingTest:^
BOOL(id obj, NSUInteger idx, BOOL *stop)
{
return [obj isEqualToString:extension];
}];
switch (index)
{
case 0:
directory = #"texts/";
break;
case 1:
directory = #"images/";
break;
case 2:
directory = #"sounds/";
break;
case 3:
directory = #"videos/";
break;
default:
#throw [NSException exceptionWithName:#"unkonwnFileFormat"
reason:[NSString stringWithFormat:#"zip file contain nknown file format: %#",fileName]
userInfo:nil];
break;
}
The technique is extracted from production code and modified to use colors for this example. The premise is that a string comes in with the text name of a color from some external feed. This inbound color name is matched against known Crayola color names in the system. If the new color name matches any known Crayola color name strings, the numeric value for HTML hex code equivalent of that Crayola color name is returned.
First use http://www.unit-conversion.info/texttools/crc/ and put all of your known Crayola color names through it to get numerical equivalents. These will be used in the case statements. Then put those values into an enumerated for cleanliness (e.g. LivingColors below). These numbers become equivalent to the actual color name string.
Then at run time the variable text is put through the same function, but internal to your code, to generate the same kind of numeric constant. If the numeric constant from the code matches the statically generated constant, then the text strings that they represent are exactly equal.
The internal code function is crc32() found in zlib.h. This generates a unique number based upon the text put through it just like the web page converter above. The unique number from crc32() can then be used in a common C switch() statement to match against the known colors which were pre-processed into numbers into the enumerated.
To use the native system function crc32() to generate CRC32B values, include the /usr/lib/libz.1.dylib in your project for linking. Be sure to include or #import <zlib.h> in your source that references crc32()
Implement an Objective C category on NSString to make the native NSString class understand the crc32: and htmlColor: messages.
Finally, read/get the name of the color into an NSString object, then send the string the htmlColor: message, it switches to match the 'strings' and returns the HTML hex equivalent value for a Crayola color name.
#import <zlib.h>
#define typedefEnum( enumName ) typedef enum enumName enumName; enum enumName
/**
#see Crayola Web Colors https://www.w3schools.com/colors/colors_crayola.asp
#see CRC32B value generator for static case strings http://www.unit-conversion.info/texttools/crc/ or http://www.md5calc.com
*/
#define typedefEnum( enumName ) typedef enum enumName enumName; enum enumName
typedefEnum( LivingColors ) {
kRedColor = 0xc22c196f, // "Red" is 0xED0A3F in HTML
kBlueberryColor = 0xfbefa670, // "Blueberry" is 0x4F86F7 in HTML
kLightChromeGreenColor = 0x44b77242, // "Light Chrome Green" is 0xBEE64B in HTML
kPermanentGeraniumLakeColor = 0xecc4f3e4, // "Permanent Geranium Lake" is 0xE12C2C in HTML
kIlluminatingEmeraldColor = 0x4828d5f2, // "Illuminating Emerald" is 0x319177 in HTML
kWildWatermelonColor = 0x1a17c629, // "Wild Watermelon" is 0xFD5B78 in HTML
kWashTheDogColor = 0xea9fcbe6, // "Wash the Dog" is 0xFED85D in HTML
kNilColor = 0xDEADBEEF // could use '0' but what fun is that?
};
// generates the CRC32B, same used to check each ethernet packet on the network you receive so it’s fast
- (NSUInteger) crc32 {
NSUInteger theResult;
theResult = (NSUInteger)crc32( 0L,
(const unsigned char *) [self UTF8String],
(short)self.length);
return theResult;
}
/// #return the HTML hex value for a recognized color name string.
- (NSUInteger) htmlColor {
NSUInteger theResult = 0x0;
LivingColors theColorInLivingColor = kNilColor;
theColorInLivingColor = (LivingColors) [self crc32];
// return the HTML value for a known color by effectively switching on a string.
switch ( theColorInLivingColor ) {
case kRedColor : {
theResult = 0xED0A3F;
}
break;
case kBlueberryColor : {
theResult = 0x4F86F7;
}
break;
case kLightChromeGreenColor : {
theResult = 0xBEE64B;
}
break;
case kPermanentGeraniumLakeColor : {
theResult = 0xE12C2C;
}
break;
case kIlluminatingEmeraldColor : {
theResult = 0x319177;
}
break;
case kWildWatermelonColor : {
theResult = 0xFD5B78;
}
break;
case kWashTheDogColor : {
theResult = 0xFED85D;
}
break;
case kNilColor :
default : {
theResult = 0x0;
}
break;
}
return theResult;
}
For the example an Objective C Category was made to add the two methods the existing Cocoa class NSString, rather than subclass it.
The end result is that an NSString object appears to have the ability to natively get a CRC32B value of itself (very handy beyond this example) and can essentially switch() on the color’s name string that possibly came in from the user, a text file, etc. to identify a match much faster than any text string comparison can occur.
Fast, efficient, and reliable, this approach can easily be adapted to any kind of variable text matching to static known value text. Bear in mind that CRC32B checksums are generated by bitwise operations and the C switch statement use bitwise operations optimized at compile time. Remember this is speedy because CRC32B is the highly optimized function used to check each ethernet packet your Mac/iPhone/iPad receives... even when you download multi-gigabyte files like macOS Sierra.
The reason is I must get back the exact value as it was in the property. So if it was a float, I want to call -floatValue. But if it was an int, I want to call -intValue.
Is NSNumber remembering how it was initialized?
NSNumber is toll-free bridged with CFNumber (see, amongst other sources, the text at the top of the CFNumber reference). So you can use CFNumberGetType. E.g.
- (void)logTypeOf:(NSNumber *)number
{
switch(CFNumberGetType((CFNumberRef)number))
{
case kCFNumberSInt8Type: NSLog(#"8bit signed integer"); break;
case kCFNumberSInt16Type: NSLog(#"16bit signed integer"); break;
case kCFNumberSInt32Type: NSLog(#"32bit signed integer"); break;
/* ... etc, for all of:
kCFNumberSInt64Type
kCFNumberFloat32Type
kCFNumberFloat64Type
kCFNumberCharType
kCFNumberShortType
kCFNumberIntType
kCFNumberLongType
kCFNumberLongLongType
kCFNumberFloatType
kCFNumberDoubleType
kCFNumberCFIndexType
kCFNumberNSIntegerType
kCFNumberCGFloatType
*/
}
}
EDIT: looking more thoroughly at the documentation, CFNumberIsFloatType would appear to do exactly what you want without the complexity. So:
if(CFNumberIsFloatType((CFNumberRef)number))
{
NSLog(#"this was a float");
}
else
{
NSLog(#"this was an int");
}