#import <Foundation/Foundation.h>
int main(int argc, const char * argv[])
{
#autoreleasepool {
NSMutableString *outputStringSet = [[NSMutableString alloc] init];
NSMutableString *outputStringArray = [[NSMutableString alloc] init];
NSMutableSet *mySet = [[NSMutableSet alloc] init];
NSMutableArray *myArray = [[NSMutableArray alloc] initWithCapacity: 10];
int userInput;
NSLog(#"Enter 10 numbers");
for( int i = 0; i < 10; i++) {
scanf("%i", &userInput);
NSNumber *input = [[NSNumber alloc] initWithInt: userInput];
[myArray addObject:input];
if([mySet member: input]) {
[mySet addObject: input];
}
}
for (int k = 0; k < [myArray count]; k++) {
[outputStringArray appendFormat:#"%#, ", [myArray objectAtIndex:k]];
}
NSLog(#"%#", [outputStringArray substringToIndex:[outputStringArray length] - 2]);
for (int j = 0; j < [myArray count]; j++) {
if([mySet containsObject: [myArray objectAtIndex:j]]) {
[outputStringSet appendFormat:#"%#, ", [myArray objectAtIndex:j]];
}
NSLog(#"%#", outputStringSet);
}
}
return 0;
}
Code above prints the array but not the appropriate object in the set
Why?
Please explain clearly. I am a bit of a noob, and couldnt find the answer anywhere else.
thanks
if([mySet member: input]) {
[mySet addObject: input];
}
You're adding the object to the set if it’s already in it. You want the reverse: add the object if it's not in it.
Thus:
if ( ! [mySet member:input] )
[mySet addObject:input];
By the way, you should use containsObject: instead of member: in your test:
containsObject:
Returns a Boolean value that indicates whether a given
object is present in the set.
- (BOOL)containsObject:(id)anObject
Edit: you don't even need to test if the object is already in the set before adding it. After all, that's the main purpose of a NSSet: to ensure uniqueness of its objects. So if you add an object twice, the second call will silently be ignored, as the object is alreay in it.
Your set is empty because of
if([mySet member: input]) {
[mySet addObject: input];
}
member:
Determines whether the set contains an object equal to a given object,
and returns that object if it is present.
Related
I'm learning Objective-C runtime, and try to use method_exchangeImplementations to exchange addObject: method and removeObject: method of NSMutableArray.
My code like this:
int main(int argc, const char * argv[]) {
#autoreleasepool {
Method removeMethod = class_getInstanceMethod(NSMutableArray.class, #selector(removeObject:));
Method addMethod = class_getInstanceMethod(NSMutableArray.class, #selector(addObject:));
method_exchangeImplementations(addMethod, removeMethod);
NSMutableArray *array = [[NSMutableArray alloc] init];
NSObject *obj = [[NSObject alloc] init];
[array removeObject:obj];
NSLog(#"%lu", (unsigned long)array.count); // expect print 1, actual print 1
[array addObject:obj];
NSLog(#"%lu", (unsigned long)array.count); // expect print 0, actual print 2
}
return 0;
}
I expect exchange add/remove function, but seems like only removeObject: has been exchange to addObject: , addObject: still is addObject to array, now I have two addObject method of NSMutableArray
I'm not sure the reason. I try to exchange other method like uppercaseString/lowercaseString of NSString, that work correct.
OK, I solved problem. Thanks #Willeke for the tip.
The real class of my array is not NSMutableArray, so use NSMutableArray.class in class_getInstanceMethod can't get correct method. Use [array class] is the answer.
int main(int argc, const char * argv[]) {
#autoreleasepool {
NSMutableArray *array = [[NSMutableArray alloc] init];
Method removeMethod = class_getInstanceMethod([array class], #selector(removeObject:));
Method addMethod = class_getInstanceMethod([array class], #selector(addObject:));
method_exchangeImplementations(addMethod, removeMethod);
NSObject *obj = [[NSObject alloc] init];
[array removeObject:obj];
NSLog(#"%lu", (unsigned long)array.count); // expect print 1, actual print 1
[array addObject:obj];
NSLog(#"%lu", (unsigned long)array.count); // expect print 0, actual print 0
}
return 0;
}
I have an NSmutable array and I am adding some strings present in the C array to it. By using this method
if (!self.arrayOfVariableNames) {
self.arrayOfVariableNames = [[NSMutableArray alloc] init];
for (int i = 0; i< cols; i++) {
[self.arrayOfVariableNames addObject:[NSString stringWithCString:cArrayOfVariableNames[i] encoding:NSUTF8StringEncoding ]];
}
}
else{
[self.arrayOfVariableNames removeAllObjects];
for (int i = 0; i< cols; i++) {
[self.arrayOfVariableNames addObject:[NSString stringWithCString:cArrayOfVariableNames[i] encoding:NSUTF8StringEncoding ]];
}
}
Does this method ensure that the objects in the NSmutableArray won't be deallocated when the C array is taken out of memory?
if this array arrayOfVariableNames is becoming Null, then the problem is with the initialisation of the array. Please try to use Lazy loading by doing this:
- (NSArray*)arrayOfVariableNames {
if (!_arrayOfVariableNames) {
_arrayOfVariableNames = [[NSMutableArray alloc] init]; //initialise the array if needed
}
return _arrayOfVariableNames; //else return the already initialized array
}
and please comment out this line in your code: self.arrayOfVariableNames = [[NSMutableArray alloc] init];
****EDIT****
Please find the update code in https://docs.google.com/file/d/0BybTW7Dwp2_vdHhQN1p1UzExdTA/edit?pli=1. Have a look at it.
Yes. NSArray retains anything in it.
But you should stop chaining your NSString creation and instead creat a string a line before adding it to the array. Then check for nil.
Only add it to the array if it is not nil.
Do code defensively.
arrayOfVariableNames will not change when the C array get deallocated.
Make sure that your arrayOfVariableNames variable is strong.
#property (nonatomic, strong) NSMutableArray *arrayOfVariableNames;
if (!self.arrayOfVariableNames)
{
self.arrayOfVariableNames = [[NSMutableArray alloc] init];
}
else
{
[self.arrayOfVariableNames removeAllObjects];
}
for (int i = 0; i< cols; i++)
{
NSString *tempString = [NSString stringWithCString:cArrayOfVariableNames[i] encoding:NSUTF8StringEncoding];
if([tempString length] > 0)
{
[self.arrayOfVariableNames addObject:tempString];
}
else
{
NSLog(#"string is empty");
}
}
I stored some strings in objects and added the objects to an NSMutableArray. Now I want to print the strings in each element of the array. Clearly, I'm doing something wrong. I'm going to back and review these basics, but I was hoping someone could explain how I can print the string instead of the what looks to be the element address.
/** interface **/
#property (nonatomic, copy) NSString*myNumber;
-(void)setNumber: (NSString*) randomNumber;
/** implementation **/
#synthesize myNumber;
-(void) setNumber:(NSString *)randomNumber
{
myNumber = randomNumber;
}
/**main**/
Fraction * aFrac = [[Fraction alloc] init];
[aFrac setNumber:#"5/6"];
Fraction * bFrac = [[Fraction alloc] init];
[bFrac setNumber:#"2/3"];
NSMutableArray * myArray = [[NSMutableArray alloc] init];
[myArray addObject:aFrac];
[myArray addObject:bFrac];
int i;
for(i = 0; i<2; ++i)
{
id myArrayElement = [myArray objectAtIndex:i];
NSLog(#"%#", myArrayElement);
}
for(i = 0; i<2; ++i)
{
NSLog(#"%#", myArray[i]);
}
Both for loops print the same thing.
When you pass a custom object to NSLog you have to override the -(NSString)description method in that object.
So in your Fraction class if you simply override this function like so
- (NSString*)description
{
return self.myNumber;
}
that should log out what you want.
I would probably think about renaming that property from number as you are storing a string.
Hope that helps
I'm guessing the Fraction type you created has a NSString property or method named number (to match the -setNumber: method), in which case you would use the following code to print it:
NSLog("%#", [myArrayElement number]);
Or, for the second loop:
NSLog("%#", [myArray[i] number]);
In your code both for loop meaning has same only, try below
for(i = 0; i<2; ++i)
{
id myArrayElement = [myArray objectAtIndex:i];
NSLog(#"%#", myArrayElement.number);
}
for(i = 0; i<2; ++i)
{
NSLog(#"%#", myArray[i].number);
}
Now here two array value you are extracting
[myArray objectAtIndex:i] which is equivalent to myArray[i]
Okay, so, I'm doing a simple lookup. I have an array of NSString objects and a string to search for in the array's elements.
It all seems to work up until I try to add a match to a new mutable array made to hold the search results. The stringHolder variable gets the string, and resultsCollectorArray even get the right number of new elements, but each element is empty and "out of range". Here's the method:
#implementation NSArray (checkForString)
-(NSMutableArray *) checkForString: (NSString *) matchSought
{
long unsigned numberofArrayElements;
long unsigned loop = 0;
NSRange searchResults;
NSMutableArray * resultCollectorArray = [[NSMutableSet alloc] init];
id stringHolder;
numberofArrayElements = [self count];
while (loop < numberofArrayElements) {
searchResults.length = 0;
searchResults = [[self objectAtIndex: loop] rangeOfString: matchSought options:NSCaseInsensitiveSearch];
if (searchResults.length > 0) {
stringHolder = [self objectAtIndex: loop];
[resultCollectorArray addObject: stringHolder];
}
loop++;
}
return [resultCollectorArray autorelease];
}
Once we get back to the main portion of the program, I get an unrecognized selector sent to the mutable array that was supposed to receive the result of the method. Here's the main section:
#import <Foundation/Foundation.h>
#import "LookupInArray.h"
int main (int argc, const char * argv[])
{
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
NSString *testString = [[NSString alloc] initWithString: #"ab"];
NSMutableString * resultString = [[NSString alloc] init];
NSArray * theArray = [[NSArray alloc] initWithObjects: ..., nil]; // Actual code has the objects
NSMutableArray *resultArray = [[NSMutableArray alloc] init];
NSUInteger arrayCount = 0;
unsigned long loops = 0;
resultArray = [theArray checkForString: testString];
arrayCount = [resultArray count];
while (loops < arrayCount){
resultString = [resultArray objectAtIndex: loops]; // Here's where we get the unrecognized selector.
NSLog(#"%#", resultString);
loops++;
}
[pool drain]; // Also, I'll release the objects later. I just want to get what's above working first.
return 0;
}
I've searched the other answers (for hours now), but didn't seen anything that solved the issue.
Any and all help would be really appreciated.
And thanks beforehand.
NSMutableArray * resultCollectorArray = [[NSMutableSet alloc] init]; is so incorrect. You are creating a mutable set and assigning it to a mutable array.
You are getting unrecognized selector because objectAtIndex: is not a valid selector for NSMutableSet. Make that statement,
NSMutableArray * resultCollectorArray = [[NSMutableArray alloc] init];
A Better way
NSArray * filteredArray = [array filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:#"SELF contains[cd] %#", searchString]];
You can directly filter the array using predicates. This way you do this in a single step. :)
Sorry for the simple question, but I am self taught and know that there are gaps in my education.
To print an array in objective C, I believe is:
NSLog(#"My array: %#", myArray);
How can I print an array of arrays?
Thanks
You want this:
for(NSArray *subArray in myArray) {
NSLog(#"Array in myArray: %#",subArray);
}
This will work for an array that has arrays nested one level deep.
You don't need to do anything different to log an array of arrays; the code exactly as you've written it will already show the contents of the sub-arrays.
That is, the following program:
#import <Foundation/Foundation.h>
int main (int argc, const char * argv[]) {
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
NSMutableArray *array = [NSMutableArray array];
for (int i=0; i<5; ++i) {
NSMutableArray *sub = [NSMutableArray array];
for (int j=0; j<=i; ++j) {
[sub addObject:[NSString stringWithFormat:#"%d", j]];
}
[array addObject:sub];
}
NSLog(#"Array: %#", array);
[pool drain];
return 0;
}
Produces the following output:
Array: (
(
0
),
(
0,
1
),
(
0,
1,
2
),
(
0,
1,
2,
3
),
(
0,
1,
2,
3,
4
)
)
Clearly, it's already logging the sub-arrays just fine. If you want to control the formatting differently, you'd have to manually iterate them, but by default, the -description of an NSArray is little more than the -description of every object in that array, which includes all sub-arrays.
So I was embarrassed by the recursiveDescription thing, so I wrote my own as a category on NSArray. Note that this code will print out a description for an array of arrays to any depth. The description itself could probably use a bit more formatting than commas and newlines. Here you go:
#interface NSArray (RecursiveDescription)
- (NSString *)recursiveDescription;
#end
#implementation NSArray (RecursiveDescription)
- (NSString *)recursiveDescription {
NSMutableString *description = [[NSMutableString alloc] initWithString:#"Array (\n"];
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
for (NSObject *child in self) {
if ([child respondsToSelector:#selector(recursiveDescription)]) {
[description appendFormat:#"%#,\n", [child recursiveDescription]];
}
else {
[description appendFormat:#"%#,\n", [child description]];
}
}
[pool drain];
[description appendString:#"\n)"];
return [description autorelease];
}
#end
Try logging the return value from NSArray's -description method.
NSLog(#"My array: %#", [myArray description]);
Moreover, for print all of elements
int i = 0;
int j = 0;
for(NSArray *subArray in myArray) {
NSLog(#"[%d] %#",i, subArray);
j =0;
for(NSObject *element in subArray) {
NSLog(#"[%d:%d] %#", i,j,element);
++j;
}
++i;
}
As much as I like how easy it is to log out an object in Objective-C, I didn't like seeing a 2D array as a very long list. I created a category on NSArray that prints out 2D arrays. It's not perfect and can be improved, but it has worked for me.
Header:
#interface NSArray (Logging)
- (void)log2DArray;
#end
Implementation:
#import "NSArray+Logging.h"
#implementation NSArray (Logging)
- (void)log2DArray {
NSMutableString *formattedString = [[NSMutableString alloc] init];
NSInteger longestSubarrayLength = 0;
for (NSArray *subarray in self) {
if (subarray.count > longestSubarrayLength) {
longestSubarrayLength = subarray.count;
}
}
for (int i = 0; i < longestSubarrayLength; i++) {
[formattedString appendFormat:#"\n"];
for (int j = 0; j < self.count; j++) {
NSArray *tempArray = [self objectAtIndex:j];
if (tempArray.count <= longestSubarrayLength) {
[formattedString appendFormat:#"%#\t", [tempArray objectAtIndex:i]];
} else {
[formattedString appendFormat:#"\t"];
}
}
}
NSLog(#"%#", formattedString);
}
#end
Usage:
[myArray log2DArray];
Or use recursiveDescription :)
NSLog(#"my arrays: %#", [myArray recursiveDescription]);